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%I #26 May 14 2023 02:33:29
%S 2,3,4,5,6,11,13,21,29,31,37,170,180,214,234,265,362,369,10734,14318,
%T 19679,19876,39636,48784,62517,76225,77277,83629,85519,90649,92287
%N Numbers k such that sigma(k)! - 1 is prime, where sigma is A000203.
%e 2 is a term because sigma(2) = 3. 3! - 1 = 5, a prime.
%e 6 is a term because sigma(6) = 12. 12! - 1 = 479001599, a prime.
%o (SageMath)
%o [n for n in range(1,150) if is_prime(factorial(sigma(n))-1)]
%o (PARI) isok(n) = isprime(sigma(n)!-1); \\ _Michel Marcus_, Aug 07 2019
%Y Cf. A000040, A000203, A002982, A055490, A184388.
%K nonn,more
%O 1,1
%A _Hauke Löffler_, Aug 07 2019
%E a(12)-a(24) from _Daniel Suteu_, Aug 07 2019
%E a(25)-a(31) from _Amiram Eldar_, May 14 2023
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