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A123438 Numbers n such that the denominator of n!/!n (= A000142(n)/A000166(n)) is prime. 0
4, 5, 6, 7, 10, 11, 15, 16, 34, 44, 63, 66, 168, 427, 575, 928, 1094, 1218, 1363, 1713 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Table of n, a(n) for n=1..20.

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

STATUS

approved

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Last modified January 26 16:14 EST 2023. Contains 359833 sequences. (Running on oeis4.)