A309548 Numbers k such that sigma(k)! - 1 is prime, where sigma is A000203.

2, 3, 4, 5, 6, 11, 13, 21, 29, 31, 37, 170, 180, 214, 234, 265, 362, 369, 10734, 14318, 19679, 19876, 39636, 48784, 62517, 76225, 77277, 83629, 85519, 90649, 92287

Offset: 1

Author

Hauke Löffler, Aug 07 2019

Keywords

• nonn
• more

Examples

			2 is a term because sigma(2) = 3. 3! - 1 = 5, a prime.
6 is a term because sigma(6) = 12. 12! - 1 = 479001599, a prime.
		

Crossrefs

Cf. A000040, A000203, A002982, A055490, A184388.

Programs

PARI

isok(n) = isprime(sigma(n)!-1); \\ Michel Marcus, Aug 07 2019

SageMath

[n for n in range(1,150) if is_prime(factorial(sigma(n))-1)]

Extensions

a(12)-a(24) from Daniel Suteu, Aug 07 2019

a(25)-a(31) from Amiram Eldar, May 14 2023