+0  
 
+1
208
3
avatar+41 

(a^(n)b - ab^(n))/(2n)

 

When a and b are integers, and when the result is an integer too, i predict n is a prime number.

How can I prove it?

 

EDIT:

a and b mustn’t be equal to n and n mustn’t be 2.

lolomine09  Jan 24, 2018
edited by lolomine09  Jan 24, 2018
 #1
avatar+27044 
+3

"(a^(n)b - ab^(n))/(2n)

 

When a and b are integers, and when the result is an integer too, i predict n is a prime number."

 

Hmmm!

 

a = 4, b = 2, n = 4 gives (anb - abn)/(2n) = 56

 

a, b and (anb - abn)/(2n) are all integers, but n isn't prime.

Alan  Jan 24, 2018
edited by Alan  Jan 24, 2018
 #2
avatar+41 
0

Indeed

Then

a and b must not be equal to n.

lolomine09  Jan 24, 2018
 #3
avatar+27044 
+1

You’ll need tighter constraints than that!

 

With a = 4, b = 2, n = 8, the result is 8128.  n still not prime.

Alan  Jan 24, 2018

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