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 A090660 Numbers n such that n*nextprime((n-1)!)-nextprime(n!) < 0. 4
 3, 4, 12, 28, 38, 42, 74, 78, 117, 155, 321, 341, 400, 428, 873, 1478, 6381, 26952 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 3*nextprime((3-1)!) - nextprime(3!) = 3*nextprime(2!) - nextprime(3!) = 3*2 - 7 = -1. For n>2 n!+1 is prime <==> nextprime((n+1)!)>(n+1)nextprime(n!) and we can conjecture that for n>2 if n!+1 is prime then (n+1)!+1 is not prime. LINKS MATHEMATICA NextPrim[ n_ ] := Block[ {k = n + 1}, While[ !PrimeQ[ k ], k++ ]; k ]; Select[ Range[ 260 ], #*NextPrim[ (# - 1)! ] - NextPrim[ #! ] < 0 & ] (* Robert G. Wilson v *) CROSSREFS Cf. A090661, A089014. Equals A002981 + 1. Sequence in context: A000207 A002986 A147569 * A288140 A287594 A296271 Adjacent sequences:  A090657 A090658 A090659 * A090661 A090662 A090663 KEYWORD nonn AUTHOR Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Dec 15 2003 EXTENSIONS Better description from Don Reble, Dec 20 2003 Three more terms from Robert G. Wilson v, Dec 20 2003 a(14) from Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Jan 05 2004 STATUS approved

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Last modified March 28 05:38 EDT 2020. Contains 333073 sequences. (Running on oeis4.)