

A089920


Indices of primes p such that 7^p  2 is prime.


0




OFFSET

1,2


COMMENTS

Except for p=2, 2, 5^p  2 cannot be prime. This immediately follows from the fact that a number N = (3k+2)^p  2 cannot be prime for p > 2 because N = 3H + 2^p  2 = 3H + 2(2^(p1)1) is divisible by 3.


LINKS



FORMULA



MATHEMATICA

Select[Range[500], PrimeQ[7^Prime[#]2]&] (* Harvey P. Dale, May 02 2011 *)
Position[Prime[Range[150]], _?(PrimeQ[7^#2]&)]//Flatten (* Harvey P. Dale, May 11 2016 *)


PROG

(PARI) forprime(p=2, 1e4, if(ispseudoprime(7^p2), print1(x", ")))


CROSSREFS



KEYWORD

nonn,more


AUTHOR



EXTENSIONS

Definition clarified by Harvey P. Dale, May 02 2011.


STATUS

approved



