A249400 Numbers n such that n!3 + 3 is prime, where n!3 = n!!! is a triple factorial number (A007661).

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

Table of n, a(n) for n=1..43.

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 * A347782 A226896 A175302

Adjacent sequences: A249397 A249398 A249399 * A249401 A249402 A249403

Keyword

nonn,more

Author

Robert Price, Oct 27 2014

Status

approved