A289685 Numbers k such that k!6 - 6 is prime, where k!6 is the sextuple factorial number (A085158).

17, 19, 23, 31, 37, 47, 65, 151, 157, 251, 283, 371, 391, 635, 779, 799, 1517, 1799, 3355, 24619, 40375, 40793, 53135, 79427

Offset

1,1

Comments

Corresponding primes are: 929, 1723, 21499, 1339969, 49579069, 42061737019, ...

a(25) > 10^5.

Terms > 65 correspond to probable primes.

Links

Table of n, a(n) for n=1..24.

Henri & Renaud Lifchitz, PRP Records. Search for n!6-6.

Joe McLean, Interesting Sources of Probable Primes

OpenPFGW Project, Primality Tester

Example

17!6 - 6 = 17*11*5 - 6 = 929 is prime, so 17 is in the sequence.

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[6, 50000], PrimeQ[MultiFactorial[#, 6] - 6] &]

Crossrefs

Cf. A007661, A037082, A084438, A123910, A242994.

Sequence in context: A140947 A205700 A228070 * A144487 A108266 A102325

Adjacent sequences: A289682 A289683 A289684 * A289686 A289687 A289688

Keyword

nonn,more

Author

Robert Price, Jul 09 2017

Extensions

a(23)-a(24) from Robert Price, Aug 03 2018

Status

approved