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A092970 Smallest prime of the form n!/k + 1. k < = n, or 0 if no such prime exists. 3
2, 2, 3, 7, 31, 181, 1009, 13441, 45361, 453601, 3991681, 39916801, 566092801, 10897286401, 130767436801, 2988969984001, 25406244864001, 0, 8109673360588801, 304112751022080001, 2688996956405760001 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..21.

EXAMPLE

a(10) = 453601 = 10!/8 + 1, as 10!/10 + 1 and 10!/9 + 1 are both composite.

MATHEMATICA

Table[SelectFirst[Reverse[n!/Range[n]+1], PrimeQ], {n, 30}]/.(Missing[ "NotFound"] -> 0) (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 15 2019 *)

PROG

(PARI) a(n)=for (i=1, n, if(isprime(n!/(n-i+1)+1), return((n!/(n-i+1)+1))))

CROSSREFS

Cf. A092968, A092969, A092068.

Sequence in context: A180996 A307503 A087522 * A052449 A053413 A232542

Adjacent sequences:  A092967 A092968 A092969 * A092971 A092972 A092973

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Mar 26 2004

EXTENSIONS

Corrected and extended by Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 26 2004

STATUS

approved

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Last modified October 22 06:54 EDT 2019. Contains 328315 sequences. (Running on oeis4.)