A094516 Primes p such that q=(p^2+1)/2 is not a prime.

2, 7, 13, 17, 23, 31, 37, 41, 43, 47, 53, 67, 73, 83, 89, 97, 103, 107, 109, 113, 127, 137, 149, 151, 157, 163, 167, 173, 179, 191, 193, 197, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 353, 359, 367, 373

Offset: 1

Author

N. J. A. Sloane, following a suggestion by R. K. Guy, Jun 05 2004

Keywords

• nonn

Links

• Ray Chandler, Table of n, a(n) for n = 1..10000

Crossrefs

Complement in primes of A048161.

Programs

Mathematica

Select[Prime[Range[100]],!PrimeQ[(#^2+1)/2]&] (* Harvey P. Dale, Apr 26 2017 *)

Python

from sympy import isprime
def ok(n): return (isprime(n) and (n == 2 or not isprime((n*n + 1)//2)))
print(*list(filter(ok, range(2, 360))), sep = ', ') # Ya-Ping Lu, May 01 2025