A176994 Least odd prime p such that p#*2^n-1 is prime, with p# the primorial A034386(p).

3, 3, 3, 3, 5, 3, 3, 7, 7, 5, 3, 109, 17, 5, 13, 17, 5, 3, 17, 67, 11, 89, 13, 17, 7, 89, 31, 29, 19, 37, 5, 7, 29, 3, 79, 43, 41, 3, 11, 53, 5, 13, 3, 29, 11, 137, 179, 227, 11, 11, 97, 59, 53, 11, 3, 83, 17, 47, 19, 19, 29, 73, 41, 3, 7, 11, 79, 71, 13, 41, 257, 19, 5, 151, 79, 3, 31, 19, 79, 5, 281, 5, 37, 263, 139, 17, 23, 127, 223, 151, 149, 131, 113, 3, 47, 41, 59, 31, 23, 89

Offset: 0

Author

Pierre CAMI, Dec 08 2010

Keywords

• nonn

Links

• Pierre CAMI, Table of n, a(n) for n = 0..2642

Crossrefs

Cf. A085427.

Programs

Mathematica

Table[p=3; prod=6; While[! PrimeQ[prod*2^n-1], p=NextPrime[p]; prod=prod*p]; p, {n, 0, 100}]

Sage

primorial = lambda n: prod(primes(n+1)) # includes n, if prime
A176994 = lambda n: next(p for p in Primes() if p > 2 and is_pseudoprime(primorial(p)*2**n-1)) # D. S. McNeil, Dec 09 2010