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 A309548 Numbers k such that sigma(k)! - 1 is prime, where sigma is A000203. 0
 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 (list; graph; refs; listen; history; text; internal format)
 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: A082657 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

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Last modified June 24 10:07 EDT 2024. Contains 373674 sequences. (Running on oeis4.)