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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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Large terms correspond to probable primes. a(44) > 50000. LINKS Henri & Renaud Lifchitz, PRP Records. Search for n!3-27 Joe McLean, Interesting Sources of Probable Primes 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 Cf. A007661, A037082, A084438, A243078. Sequence in context: A119905 A213219 A161750 * A226896 A175302 A288521 Adjacent sequences:  A249397 A249398 A249399 * A249401 A249402 A249403 KEYWORD nonn,more AUTHOR Robert Price, Oct 27 2014 STATUS approved

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Last modified October 22 14:44 EDT 2019. Contains 328318 sequences. (Running on oeis4.)