A033299 Smallest safe prime ((p-1)/2 is also prime) > n.

5, 5, 5, 5, 7, 7, 11, 11, 11, 11, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 47, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 59, 83, 83, 83, 83, 83, 83, 83, 83, 83

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Links

• Michael S. Branicky, Table of n, a(n) for n = 1..10000

Programs

Maple

with(numtheory); safeprime(n);

Python

from sympy import isprime, nextprime
def a(n):
  p = nextprime(n)
  while not isprime((p-1)//2): p = nextprime(p)
  return p
print([a(n) for n in range(1, 68)]) # Michael S. Branicky, May 05 2021

Extensions

a(57) and beyond from Michael S. Branicky, May 05 2021