A289687 Numbers k such that k!6 - 9 is prime, where k!6 is the sextuple factorial number (A085158).

8, 10, 16, 22, 26, 46, 52, 56, 70, 74, 286, 302, 308, 484, 698, 1100, 1226, 1528, 2486, 3796, 4256, 8524, 10688, 19424, 22226, 49346, 53746, 64178, 84304

Offset

1,1

Comments

Corresponding primes are: 7, 31, 631, 14071, 116471, 24663654391, 1282510028791, ...

a(30) > 10^5.

Terms > 46 correspond to probable primes.

Links

Table of n, a(n) for n=1..29.

Henri & Renaud Lifchitz, PRP Records. Search for n!6-9.

Joe McLean, Interesting Sources of Probable Primes

OpenPFGW Project, Primality Tester

Example

16!6 - 9 = 16*10*4 - 8 = 631 is prime, so 16 is in the sequence.

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[8, 50000], PrimeQ[MultiFactorial[#, 6] - 9] &]

Crossrefs

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

Sequence in context: A058633 A165143 A355568 * A155966 A228072 A038209

Adjacent sequences: A289684 A289685 A289686 * A289688 A289689 A289690

Keyword

nonn,more

Author

Robert Price, Jul 09 2017

Extensions

a(27)-a(29) from Robert Price, Aug 03 2018

Status

approved