if p=2 then
p^4+1=2^4+1=17
so it works for p=2
if p>2
then p is either 1 or 3 mod 4
if p=1 mod 4 then
p^4+1=1^4+1 mod 4 = 2 mod 4
and thus is divisible by 2 and not prime
if p=3 mod 4 then
p^4+1=3^4+1 mod 4=2 mod 4
and thus is divisible by 2 and not prime
Thus the only prime p for which p^4+1 is also prime is p=2.

Posted by Daniel
on 20170410 14:43:02 