A289686 Numbers k such that k!6 - 8 is prime, where k!6 is the sextuple factorial number (A085158).

9, 11, 13, 15, 19, 27, 35, 39, 45, 51, 83, 99, 105, 111, 121, 123, 127, 133, 175, 177, 213, 263, 277, 285, 339, 347, 543, 681, 743, 1069, 1965, 2379, 2613, 2629, 2911, 3767, 3879, 4789, 5493, 5819, 11559, 14555, 17831, 19705, 24867, 37535, 85089

Offset

1,1

Comments

Corresponding primes are: 19, 47, 83, 397, 1721, 229627, 21827567, ...

a(48) > 10^5.

Terms > 99 correspond to probable primes.

Links

Table of n, a(n) for n=1..47.

Henri & Renaud Lifchitz, PRP Records. Search for n!6-8.

Joe McLean, Interesting Sources of Probable Primes

OpenPFGW Project, Primality Tester

Example

19!6 - 8 = 19*13*7 - 8 = 1721 is prime, so 19 is in the sequence.

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[8, 50000], PrimeQ[MultiFactorial[#, 6] - 8] &]

Crossrefs

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

Sequence in context: A008558 A335912 A123760 * A251394 A155877 A214865

Adjacent sequences: A289683 A289684 A289685 * A289687 A289688 A289689

Keyword

nonn

Author

Robert Price, Jul 09 2017

Extensions

a(47) from Robert Price, Aug 03 2018

Status

approved