A288445 Numbers k such that k!6 + 18 is prime, where k!6 is the sextuple factorial number (A085158 ).

1, 5, 11, 13, 17, 19, 23, 31, 37, 41, 49, 83, 115, 161, 205, 617, 683, 769, 799, 1117, 1151, 1685, 1697, 1951, 2173, 3619, 3647, 6229, 6463, 6613, 9827, 12985, 15721, 16933, 22579, 25181, 38869, 48755

Offset

1,2

Comments

Corresponding primes are: 19, 23, 73, 109, 953, 1747, 21523, 1339993, 49579093, 894930593, ...

a(39) > 50000.

Terms > 49 correspond to probable primes.

Links

Table of n, a(n) for n=1..38.

Henri & Renaud Lifchitz, PRP Records. Search for n!6+18.

Joe McLean, Interesting Sources of Probable Primes

OpenPFGW Project, Primality Tester

Example

11!6 + 18 = 11*5 + 18 = 73 is prime, so 11 is in the sequence.

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[0, 50000], PrimeQ[MultiFactorial[#, 6] + 18] &]

Crossrefs

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

Sequence in context: A268476 A082554 A141246 * A087759 A234644 A299791

Adjacent sequences: A288442 A288443 A288444 * A288446 A288447 A288448

Keyword

nonn,more

Author

Robert Price, Jun 09 2017

Status

approved