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A247463 Numbers n such that n!3 - 3^3 is prime, where n!3 = n!!! is a triple factorial number (A007661). 1
8, 11, 13, 22, 29, 49, 56, 61, 103, 142, 149, 257, 319, 365, 680, 736, 737, 749, 947, 974, 1040, 4277, 4678, 9961, 10652, 15545, 18064, 31325, 34918, 41032 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Large terms correspond to probable primes.

a(31) > 50000.

LINKS

Table of n, a(n) for n=1..30.

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!3-27 = 11*8*5*2-27 = 853 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] - 27], AppendTo[lst, n]], {n, 100}]; lst

CROSSREFS

Cf. A007661, A037082, A084438, A243078.

Sequence in context: A122195 A064153 A106670 * A308562 A254671 A265412

Adjacent sequences:  A247460 A247461 A247462 * A247464 A247465 A247466

KEYWORD

nonn,more

AUTHOR

Robert Price, Sep 17 2014

STATUS

approved

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Last modified November 18 22:50 EST 2019. Contains 329305 sequences. (Running on oeis4.)