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

1,1

Links

Table of n, a(n) for n=1..31.

Example

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.

Prog

(SageMath)
[n for n in range(1, 150) if is_prime(factorial(sigma(n))-1)]
(PARI) isok(n) = isprime(sigma(n)!-1); \\ Michel Marcus, Aug 07 2019

Crossrefs

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

Sequence in context: A387039 A108378 A084588 * A088411 A075073 A157420

Adjacent sequences: A309545 A309546 A309547 * A309549 A309550 A309551

Keyword

nonn,more

Author

Hauke Löffler, Aug 07 2019

Extensions

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

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

Status

approved