A092970 Smallest prime of the form n!/k + 1. k < = n, or 0 if no such prime exists.

2, 2, 3, 7, 31, 181, 1009, 13441, 45361, 453601, 3991681, 39916801, 566092801, 10897286401, 130767436801, 2988969984001, 25406244864001, 0, 8109673360588801, 304112751022080001, 2688996956405760001

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