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A309548
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Numbers k such that sigma(k)! - 1 is prime, where sigma is A000203.
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0
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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
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OFFSET
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1,1
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LINKS
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EXAMPLE
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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.
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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