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
Keywords
Examples
a(10) = 453601 = 10!/8 + 1, as 10!/10 + 1 and 10!/9 + 1 are both composite.
Programs
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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 *) -
PARI
a(n)=for (i=1,n,if(isprime(n!/(n-i+1)+1),return((n!/(n-i+1)+1))))
Extensions
Corrected and extended by Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 26 2004