Applications of Smarandache Function, and Prime and Coprime Functions

Sebastián Martín Ruiz

Applications of Smarandache Function, and Prime and Coprime Functions

0 if C k (n1 , n 2 , L , n k ) =  1

n1 , n2 ,L , n k

are coprime numbers

otherwise

American Research Press Rehoboth 2002

SebastiĂĄn MartĂ­n Ruiz Avda. De Regla, 43, Chipiona 11550 (Cadiz), Spain

Smaranda@teleline.es www.terra.es/personal/smaranda

Applications of Smarandache Function, and Prime and Coprime Functions

American Research Press Rehoboth 2002

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This book can be ordered in microfilm format from: Bell and Howell Co. (University of Microfilm International) 300 N. Zeeb Road P.O. Box 1346, Ann Arbor MI 48106-1346, USA Tel.: 1-800-521-0600 (Customer Service) http://wwwlib.umi.com/bod/search/basic (Books on Demand)

Copyright 2002 by American Research Press Rehoboth, Box 141 NM 87322, USA http://www.gallup.unm.edu/~smarandache/math.htm

ISBN: 1-931233-30-6 Standard Address Number 297-5092 Printed in the United States of America

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Contents: Chapter 1: Smarandache Function applied to perfect numbers Chapter 2: A result obtained using the Smarandache Function Chapter 3: A Congruence with the Smarandache Function Chapter 4: A functional recurrence to obtain the prime numbers using the Smarandache prime function Chapter 5: The general term of the prime number sequence and the Smarandache prime function Chapter 6:Expressions of the Smarandache Coprime Function Chapter 7: New Prime Numbers

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Chapter 1: Smarandache function applied to perfect numbers The Smarandache function is defined as follows: S(n)= the smallest positive integer such that S(n)! is divisible by n. [1] In this article we are going to see that the value this function takes when n is a perfect number of the form n = 2 k −1 ⋅ (2 k − 1) , p = 2 k − 1 being a prime number.

Lemma 1: Let n = 2 i ⋅ p when p is an odd prime number and i an integer such that: p    p  p  p 0 ≤ i ≤ E   + E  2  + E  3  + L + E  E (log 2 p )  = e2 ( p!) 2  2  2  2 where e2 ( p!) is the exponent of 2 in the prime number decomposition of p!.

E(x) is the greatest integer less than or equal to x.

One has that S (n) = p .

Demonstration: Given that GCD (2 i , p) = 1 (GCD= greatest common divisor) one has that S (n) = max{S (2 i ), S ( p )} ≥ S ( p ) = p. Therefore S (n) ≥ p.

If we prove that p! is divisible by n then one would have the equality. p!= p1

e p1 ( p!)

⋅ p2

e p2 ( p!)

L ps

e ps ( p!)

where pi is the i − th prime of the prime number decomposition of p!. It is clear that p1 = 2, p s = p , e ps ( p!) = 1 for which: p!= 2

e ( p!)

2

⋅ p2

e p ( p!)

2

L p s −1

5

ep

s −1

( p!)

⋅p

From where one can deduce that: p! e ( p!) − i ( p!) e ( p!) e =2 2 ⋅ p 2 p2 L p s −1 ps −1 n is a positive integer since e2 ( p!) − i ≥ 0 .

Therefore one has that S (n) = p Proposition1: If n is a perfect number of the form n = 2 k −1 ⋅ (2 k − 1) with k is a positive integer, 2 k −1 = p prime, one has that S (n) = p .

Demonstration: For the Lemma it is sufficient to prove that k − 1 ≤ e2 ( p!) .

If we can prove that: k − 1 ≤ 2 k −1 −

1 2

(1)

we will have proof of the proposition since: k − 1 ≤ 2 k −1 −

1 2k −1 p = = 2 2 2

p As k − 1 is an integer one has that k − 1 ≤ E   ≤ e2 ( p!)

2 1 Proving (1) is the same as proving k ≤ 2 k −1 + at the same time, since k is 2 integer, is equivalent to proving k ≤ 2 k −1 (2).

In order to prove (2) we may consider the function: f ( x) = 2 x −1 − x x real number.

This function may be derived and its derivate is f ′( x) = 2 x −1 ln 2 − 1 . f will be increasing when 2 x −1 ln 2 − 1 > 0 resolving x: x > 1−

ln(ln 2) ≅ 1'5287 ln 2

In particular f will be increasing ∀ x ≥ 2 .

Therefore ∀ x ≥ 2

f ( x) ≥ f (2) = 0 that is to say 2 x −1 − x ≥ 0 ∀x ≥ 2 .

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Therefore: 2 k −1 ≥ k ∀k ≥ 2 integer.

And thus is proved the proposition.

EXAMPLES: 6 = 2⋅3 28 = 2 2 ⋅ 7 496 = 2 4 ⋅ 31 8128= 2 6 ⋅ 127

S(6)=3 S(28)=7 S(496)=31 S(8128)=127

References: [1] C. Dumitrescu and R. Müller: To Enjoy is a Permanent Component of Mathematics. SMARANDACHE NOTIONS JOURNAL Vol. 9 No 1-2, (1998) pp 21-26

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Chapter 2: A result obtained using the Smarandache Function Smarandache Function is defined as followed: S(m)=The smallest positive integer so that S(m)! is divisible by m. [1] n Let’s see the value which such function takes for m = p p with n integer, n≥2 and p prime number. To do so a Lemma required.

Lemma 1 ∀ m, n ∈ Ν m, n ≥ 2   n +1 n  m n +1 − m n + m   m n +1 − m n + m   m −m +m  L E + + E + mn = E     E  logm  m n +1 −m n + m    m m2     m 

where E(x) gives the greatest integer less than or equal to x.

Proof: Let’s see in the first place the value taken by

  E  log m  m n +1 − m n + m     

.

If n ≥ 2 : m n +1 − m n + m < m n +1 and therefore log m (m n +1 − m n + m ) < log m m n +1 = n + 1 .

And if m ≥ 2 : mm n ≥ 2m n ⇒ m n +1 ≥ 2m n ⇒ m n +1 + m ≥ 2m n ⇒ m n+1 − m n + m ≥ m n ⇒ log m m n +1 − m n + m ≥ log m m n = n ⇒ E log m m n +1 − m n + m ≥ n

(

[

)

)]

(

As a result: n ≤ E [log m (m n +1 − m n + m )] < n + 1 therefore:

[

)]

(

E log m m n +1 − m n + m = n if n, m ≥ 2  m n +1 − m n + m   mk  

Now let’s see the value which it takes for 1 ≤ k ≤ n : E   m n +1 − m n + m  1   n +1−k − m n− k + k −1  E  = E m k m m    

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 m n +1 − m n + m  n n −1  = m − m +1 k m  

If k=1: E 

 m n +1 − m n + m  n +1− k − m n− k  =m k m  

If 1 < k ≤ n : E 

Let’s see what is the value of the sum: k=1

mn -mn-1

…

k=2

mn-1 -mn-2

k=3

mn-2

…

…

…

m2

-m

+1

-mn-3

. . . k=n-1

. . .

k=n

m

-1

Therefore: n

 m n +1 − m n + m  n =m k m  

∑ E

k =1

Proposition:

∀

m, n ≥ 2

p prime number ∀n ≥ 2 : n

S ( p p ) = p n +1 − p n + p

Proof: Having e p (k ) = exponent of the prime number p in the prime decomposition of k.

We get:    k   k  k k e p (k ) = E   + E  2  + E  3  + L + E  E (log p k )  p   p p  p    9

And using the lemma we have

[(

ep p

n +1

   p n +1 − p n + p   p n +1 − p n + p  p n +1 − p n + p   n − p + p ! = E  + E  + L + E  E  log  p n +1 − p n + p    = p 2 p p p        p   

)]

n

Therefore:

(p

n +1

p

And :

) ∈Ν

− pn + p ! pn

and

(p

n +1

p

( )= p

S pp

n

n +1

) ∉Ν

− pn + p −1 ! pn

− pn + p

References: [1] C. Dumitrescu and R. Müller: To Enjoy is a Permanent Component of Mathematics. SMARANDACHE NOTIONS JOURNAL VOL 9:, No. 1-2 (1998) pp 21-26.

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Chapter 3: A Congruence with the Smarandache function Smarandache’s function is defined thus: S(n)= is the smallest integer such that S(n)! is divisible by n. [1] In this article we are going to look at the value that has S(2k –1) (mod k) For all integer, 2 ≤ k ≤ 97 . k

S(2k-1)

S(2k-1) (mod k)

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

3 7 5 31 7 127 17 73 31 89 13 8191 127 151 257 131071 73 524287 41 337 683 178481 241 1801 8191 262657 127 2089 331

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 15 1 1

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k

S(2k-1)

31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68

2147483647 1 65537 1 599479 1 131071 1 122921 1 109 1 616318177 1 524287 1 121369 1 61681 1 164511353 1 5419 1 2099863 1 2113 1 23311 1 2796203 1 13264529 1 673 1 4432676798593 1 4051 1 131071 1 8191 27 20394401 1 262657 1 201961 1 15790321 1 1212847 1 3033169 1 3203431780337 1 1321 1 2305843009213693951 1 2147483647 1 649657 1 6700417 1 145295143558111 1 599479 1 761838257287 1 131071 35 12

S(2k-1) (mod k)

k

S(2k-1)

S(2k-1) (mod k)

69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97

10052678938039 122921 212885833 38737 9361973132609 616318177 10567201 525313 581283643249112959 22366891 1113491139767 4278255361 97685839 8831418697

1 1 1 1 1 1 1 1 1 1 1 1 1 1 57912614113275649087721 1 14449 1 9520972806333758431 1 2932031007403 1 9857737155463 1 2931542417 1 618970019642690137449562111 1 18837001 1 23140471537 1 2796203 47 658812288653553079 1 165768537521 1 30327152671 1 22253377 1 13842607235828485645766393 1

One can see from the table that there are only 4 exceptions for 2 ≤ k ≤ 97

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We can see in detail the 4 exceptions in a table: k=28=22—7 k=52=22—13 k=68=22—17 k=92=22—23

S(228-1)h15 (mod 28 ) S(252-1)h27 (mod 52 ) S(268-1)h35 (mod 68 ) S(292-1)h47 (mod 92)

One can observe in these 4 cases that k=22p with p is a prime and more k 2

over S (2 k − 1) ≡ + 1 (mod k ) UNSOLVED QUESTION: One can obtain a general formula that gives us, in function of k the value S (2 k − 1) (mod k ) for all positive integer values of k?.

Reference: [1] Smarandache Notions Journal, Vol. 9, No. 1-2, (1998), pp. 21-26.

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Chapter 4: A functional recurrence to obtain the prime numbers using the Smarandache prime function.

Theorem: We are considering the function: For n integer:   i   i   i − 1    2 −   ∑    −    2n m   j =1   j   j    F ( n) = n + 1 + ∑ ∏  −  −  i m = n +1 i = n +1        

one has: p k +1 = F ( p k ) for all k ≥ 1 where {p k }k ≥1 are the prime numbers and x  is the greatest integer less than or equal to x.

Observe that the knowledge of p k +1 only depends on knowledge of p k and the knowledge of the fore primes is unnecessary.

Proof: Suppose that we have found a function P(i ) with the following property:

1 if i is composite P(i ) =  0 if i is prime

This function is called Smarandache prime function.(Ref.) Consider the following product: m

∏ P(i)

i = pk +1

If p k < m < p k +1

m

∏ P(i) = 1 since i : p k +1 ≤ i ≤ m are all composites.

i = pk +1

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m

If m ≥ p k +1

∏ P (i) = 0

i = p k +1

since P( p k +1 ) = 0

Here is the sum: 2 pk

∑

m

pk +1 −1

∏ P(i) = ∑

m = pk +1 i = pk +1

2 pk

m

∏ P(i) + ∑

m = pk +1 i = pk +1

m

pk +1 −1

∏ P(i ) = ∑ 1 =

m = pk +1 i = pk +1

m = pk +1

= p k +1 − 1 − ( p k + 1) + 1 = p k +1 − p k − 1 The second sum is zero since all products have the factor P ( p k +1 ) = 0.

Therefore we have the following recurrence relation: 2 pk

p k +1 = p k + 1 + ∑

m

∏ P(i )

m = pk +1 i = pk +1

Let’s now see we can find P(i ) with the asked property.

Consider:

 i   i − 1 1 si j | i  j  −  j  = 0 si j not | i      We deduce of this relation: i i   i − 1 d (i ) = ∑   −   j =1  j   j 

where d (i) is the number of divisors of i .

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j = 1,2,L , i i ≥ 1

If i is prime d (i ) = 2 therefore:  d (i ) − 2  − −  = 0 i 

If i is composite d (i ) > 2 therefore: 0<

d (i ) − 2  d (i ) − 2  < 1 ⇒ − −  =1 i i  

Therefore we have obtained the Smarandache Prime Function P(i ) which is:

  i   i   i − 1   − 2  ∑    −    j =1  j   j   P(i ) = − −   i    

i ≥ 2 integer

With this, the theorem is already proved .

References: [1] E. Burton, “Smarandache Prime and Coprime functions”. www.gallup.unm.edu/~Smarandache/primfnct.txt [2]F. Smarandache, “Collected Papers”, Vol II 200, p.p. 137, Kishinev University Press, Kishinev, 1997.

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Chapter 5: The general term of the prime number sequence and the Smarandache prime function.

Let is consider the function d(i) = number of divisors of the positive integer number i . We have found the following expression for this function: i i  i − 1 d (i ) = ∑ E   − E   k =1  k   k 

“E(x) =Floor[x]”

We proved this expression in the article “A functional recurrence to obtain the prime numbers using the Smarandache Prime Function”.

We deduce that the folowing function:  d (i ) − 2  G (i ) = − E −  i 

This function is called the Smarandache Prime Function (Reference) It takes the next values: 0 if G (i ) =  1 if

i is

prime

i is composite

Let is consider now π (n) = number of prime numbers smaller or equal than n.

It is simple to prove that: n

π (n) = ∑ (1 − G (i)) i=2

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Let is have too: If If

 π (k )  E =0  n   π (k )  E  =1  n 

1 ≤ k ≤ pn − 1 ⇒ Cn ≥ k ≥ pn ⇒

We will see what conditions have to carry C n .

Therefore we have the following expression for p n n-th prime number: Cn  π (k )  p n = 1 + ∑ (1 − E  ) k =1  n 

If we obtain C n that only depends on n , this expression will be the general term of the prime numbers sequence, since π is in function with G and G does with d(i) that is expressed in function with i too. Therefore the expression only depends on n.

Let is consider C n = 2(E (n log n ) + 1) Since p n ≈ n log n from of a certain n0 it will be true that (1) p n ≤ 2( E (n log n) + 1) If n0 it is not too big, we can prove that the inequality is true for smaller or equal values than n0 .

It is necessary to that:  π (2( E (n log n) + 1))  E  =1 n  

If we check the inequality: (2)

π (2( E (n log n) + 1)) < 2n

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We will obtain that: π (C n )  π (C n )   π (C n )  ≤ 1 ; C n ≥ pn ⇒ E  < 2 ⇒ E  =1  n  n   n 

We can experimentaly check this last inequality saying that it checks for a lot of values and the difference tends to increase, wich makes to think that it is true for all n .

Therefore if we prove that the (1) and (2) inequalities are true for all n which seems to be very probable; we will have that the general term of the prime numbers sequence is:

    j     k   s∑=1( E ( j / s ) − E (( j − 1) / s )) − 2       ∑ 1 + E −   j   j =2     2 ( E ( n log n ) +1)         pn = 1 + 1 − E  ∑  n k =1                

Reference: [1] E. Burton, “Smarandache Prime and Coprime Functions” Http://www.gallup.unm.edu/~Smarandache/primfnct.txt [2] F. Smarandache, “Collected Papers”, Vol. II, 200 p.,p.137, Kishinev University Press.

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Chapter 6: Expressions of the Smarandache Coprime Function Smarandache Coprime function is defined this way: 0 if C k (n1 , n 2 , L , n k ) =  1

n1 , n 2 , L , n k

are coprime numbers

otherwise

We see two expressions of the Smarandache Coprime Function for k=2.

EXPRESSION 1:  n n − lcm(n1 , n 2 )  C 2 ( n1 , n2 ) = −  − 1 2  n1n 2  

x 

=the biggest integer number smaller or equal than x.

If n1 , n2 are coprime numbers: lcm(n1 , n2 ) = n1 n2 therefore:

 0  C 2 (n1 , n2 ) = −  =0  n1 n2 

If n1 , n2 aren’t coprime numbers:

lcm( n1 , n2 ) < n1 n2 ⇒ 0 <

n1n2 − lcm( n1 , n2 ) < 1 ⇒ C 2 (n1 , n 2 ) = 1 n1 n2

EXPRESSION 2:   ∏ d − d'   d∏ |n1 d '|n2   d >1 d '>1 C 2 (n1 , n 2 ) = 1 + −   ∏ ∏ (d + d ' )    d |n1 d |n2  

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If n1 , n2 are coprime numbers then d ≠ d ' ∀d , d ' ≠ 1

∏ ∏ d − d'

⇒0<

d |n1 d '|n2 d >1 d '>1

∏ ∏ (d + d ' )

< 1 ⇒ C 2 (n1 , n 2 ) = 0

d |n1 d |n2

If n1 , n2 aren’t coprime numbers ∃ d = d ' d > 1, d ' > 1 ⇒ C 2 (n1 , n2 ) = 1 EXPRESSION 3: Smarandache Coprime Function for k ≥ 2 :   1 − 1 C k (n1 , n 2 , L , nk ) = −   GCD(n1 , n 2 ,L , n k ) 

If n1 , n2 , L, nk are coprime numbers: GCD(n1 , n 2 , L , n k ) = 1 ⇒ C k (n1 , n 2 , L , nk ) = 0

If n1 , n2 , L, nk aren’t coprime numbers: GCD(n1 , n2 , L, nk ) > 1 0<

1  1  < 1 ⇒ − − 1 = 1 = C k (n1 , n2 ,L , n k ) GCD  GCD 

References: 1. E. Burton, “Smarandache Prime and Coprime Function” 2. F. Smarandache, “Collected Papers”, Vol II 22 p.p. 137,Kishinev University Press.

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Chapter 7: New Prime Numbers I have found some new prime numbers using the PROTH program of Yves Gallot.

This program in based on the following theorem: Proth Theorem (1878): Let N = k ⋅ 2 n + 1 where k < 2 n . If there is an integer number a so that N −1 a 2

≡ −1 (mod N ) therefore N is prime.

The Proth progam is a test for primality of greater numbers defined as k ⋅ b n + 1 or k ⋅ b n − 1 . The program is made to look for numbers of less than 5.000000 digits and it is optimized for numbers of more than 1000 digits..

Using this Program, I have found the following prime numbers: 3239 ⋅ 212345 + 1

with 3720 digits with 3721 digits with 3721 digits with 3713 digits

7551⋅ 212345 + 1 7595 ⋅ 2

12345

+1

9363 ⋅ 212321 + 1

a = 3, a = 7 a = 5, a = 7 a = 3, a = 11 a = 5, a = 7

Since the exponents of the first three numbers are Smarandache number Sm(5)=12345 we can call this type of prime numbers, prime numbers of Smarandache .

Helped by the MATHEMATICA progam, I have also found new prime numbers which are a variant of prime numbers of Fermat. They are the following: n

n

n

n

2 2 ⋅ 3 2 − 2 2 − 3 2 for n=1, 4, 5, 7 .

It is important to mention that for n=7 the number which is obtained has 100 digits.

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Chris Nash has verified the values n=8 to n=20, this last one being a number of 815.951 digits, obtaining that they are all composite. All of them have a tiny factor except n=13.

References: 1. Micha Fleuren, â&#x20AC;&#x153;Smarandache Factors and Reverse Factorsâ&#x20AC;?, Smarandache Notions Journal, Vol. 10, www.gallup.unm.edu/~smarandache/ 2. Chris Caldwell, The Prime Pages, www.utm.edu/research/primes

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A book for people who love numbers: Smarandache Function applied to perfect numbers, congruences.

Also, the Smarandache Prime and Coprime functions in connection with the expressions of the prime numbers.

$5.95

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