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A249400
Numbers n such that n!3 + 3 is prime, where n!3 = n!!! is a triple factorial number (A007661).
1
2, 4, 5, 7, 8, 10, 11, 13, 14, 16, 19, 20, 26, 28, 29, 32, 41, 56, 61, 77, 100, 169, 181, 205, 338, 347, 955, 1952, 2197, 2428, 2960, 3430, 4618, 7478, 8209, 8422, 9235, 11107, 13481, 18194, 19229, 29854, 46532
OFFSET
1,1
COMMENTS
Large terms correspond to probable primes.
a(44) > 50000.
LINKS
Henri & Renaud Lifchitz, PRP Records. Search for n!3-27
OpenPFGW Project, Primality Tester
Eric Weisstein's World of Mathematics, Multifactorial
EXAMPLE
11!3+3 = 11*8*5*2+3 = 883 is prime, so 11 is in the sequence.
MATHEMATICA
MultiFactorial[n_, k_] := If[n < 1, 1, If[n < k + 1, n, n*MultiFactorial[n - k, k]]];
lst={}; Do[If[PrimeQ[MultiFactorial[n, 3] + 3], AppendTo[lst, n]], {n, 100}]; lst
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Oct 27 2014
STATUS
approved