A261316 Numbers n such that n!!! - 3^n is prime.

68, 88, 91, 118, 131, 151, 157, 194, 203, 424, 602, 772, 832, 884, 947, 1309, 1463, 2246, 3304, 4043, 5725, 6683, 9344, 10969, 11026, 11735, 13664, 14857, 18529, 21676, 28217, 28793, 29605, 33206, 41182, 43777, 49936

Offset

1,1

Comments

n!!! is the triple factorial sometimes written n!3.

If taking absolute values: 1,2,5,8,13,26,29,31,41,43,44,46,56,59 would also be in this sequence.

a(38) > 50000.

Links

Table of n, a(n) for n=1..37.

Example

68 is in the sequence because 68!!!-3^68=350834017732995704466119535768239 is prime.

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, If[n < k + 1, n, n*MultiFactorial[n - k, k]]];
Select[Range[0, 100], MultiFactorial[#, 3] - 3^# > 0 && PrimeQ[MultiFactorial[#, 3] - 3^#] &]

Crossrefs

Cf. A007661, A124248, A124249.

Sequence in context: A043256 A044036 A341179 * A045268 A352040 A217776

Adjacent sequences: A261313 A261314 A261315 * A261317 A261318 A261319

Keyword

nonn

Author

Robert Price, Aug 14 2015

Status

approved