A055493 Numbers n such that Sum_{k=1..n} k! - 2 is prime.

3, 4, 5, 12, 13, 19, 65, 90, 123, 211, 281, 459

Offset

1,1

Comments

There are no further terms in this sequence because for all n >= 466 (Sum_{k=1..n} k!) - 2 is divisible by 467. [From Dmitry Kamenetsky, Feb 10 2009]

Links

Table of n, a(n) for n=1..12.

Example

1! + 2! + 3! + 4! + 5! -2 = 1 + 2 + 6 + 24 + 120 - 2 = 151 which is a prime.

Mathematica

Do[If[PrimeQ[Sum[m!, {m, 1, n}]-2], Print[n]], {n, 1, 2500}]
Flatten[Position[Accumulate[Range[500]!]-2, _?PrimeQ]] (* Harvey P. Dale, Nov 15 2014 *)

Crossrefs

Sequence in context: A296966 A235598 A191197 * A109350 A239356 A077034

Adjacent sequences: A055490 A055491 A055492 * A055494 A055495 A055496

Keyword

nonn,fini,full

Author

Robert G. Wilson v, Jul 05 2000

Status

approved