A245048 - OEIS

%I #24 Jul 26 2014 10:29:00

%S 3,5,11,13,17,19,23,41,43,47,53,67,79,83,89,97,109,131,137,149,157,

%T 163,167,179,181,193,211,223,239,241,251,263,277,281,311,317,331,379,

%U 397,401,409,421,431,439,443,449,457,467,479,541,569,599,643,647,673

%N Primes p such that p^2 + 28 is prime.

%C 7 of the first 8 odd primes are in this list.

%H Chai Wah Wu, <a href="/A245048/b245048.txt">Table of n, a(n) for n = 1..2000</a>

%e 3 is in the sequence because 3^2 + 28 = 37, which is also prime.

%e 5 is in the sequence because 5^2 + 28 = 53, which is also prime.

%e 7 is not in the sequence because 7^2 + 28 = 77 = 7 * 11.

%p A245048:=n->`if`(isprime(n) and isprime(n^2+28), n, NULL): seq(A245048(n), n=1..10^3); # _Wesley Ivan Hurt_, Jul 24 2014

%t Select[Prime[Range[200]], PrimeQ[#^2 + 28] &] (* _Alonso del Arte_, Jul 12 2014 *)

%o (Python)

%o import sympy

%o [sympy.prime(n) for n in range(1,10**6) if sympy.ntheory.isprime(sympy.prime(n)**2+28)]

%Y Cf. A062324 (p^2+4), A062718(p^2+6), A243367(p^2+10).

%K nonn

%O 1,1

%A _Chai Wah Wu_, Jul 10 2014