A290116 Primes of the form k! / 2 - 1.

2, 11, 59, 359, 181439, 4111419327088961408862781439999999, 16726263306581903554085031026720375832575999999999

Offset: 1

Author

Robert Price, Jul 19 2017

Keywords

• nonn

Examples

			6! / 2 - 1 = 359, which is prime, so 359 is in the sequence.
7! / 2 - 1 = 2519 = 11 * 229, so 2519 is not in the sequence.
		

Links

• Robert Price, Table of n, a(n) for n = 1..7
• Joe McLean, Interesting Sources of Probable Primes
• OpenPFGW Project, Primality Tester

Crossrefs

Cf. A082671, A139172.

Programs

Mathematica

Select[Table[k! / 2 - 1, {k, 2, 100}], PrimeQ[#]&]

Formula

a = (A082671(n)!-2)/2.