A123438 Numbers k such that the denominator of k!/!k (= A000142(k)/A000166(k)) is prime.

4, 5, 6, 7, 10, 11, 15, 16, 34, 44, 63, 66, 168, 427, 575, 928, 1094, 1218, 1363, 1713, 5278, 10814

Offset

1,1

Comments

That is, numbers k such that A053557(k) is prime. - Michel Marcus, Aug 28 2013

Links

Table of n, a(n) for n=1..22.

Mathematica

a[n_] := Sum[(-1)^k/k!, {k, 0, n}]; Select[Range[100], PrimeQ[Numerator[a[#]]] &] (* G. C. Greubel, Oct 31 2017 *)

Prog

(PARI) isok(n) = isprime(numerator(sum(k=0, n, (-1)^k/k!))); \\ Michel Marcus, Aug 28 2013

Crossrefs

Cf. A000142, A000166, A053557.

Sequence in context: A172999 A354489 A284371 * A039024 A065028 A107756

Adjacent sequences: A123435 A123436 A123437 * A123439 A123440 A123441

Keyword

nonn,more

Author

Ed Pegg Jr, Jul 11 2008

Extensions

a(16)-a(20) from G. C. Greubel, Nov 01 2017

a(21)-a(22) from Michael S. Branicky, Dec 16 2024

Status

approved