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A090660
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Numbers n such that n*nextprime((n-1)!)-nextprime(n!) < 0.
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3
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3, 4, 12, 28, 38, 42, 74, 78, 117, 155, 321, 341, 400, 428, 873, 1478, 6381, 26952
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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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.
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MATHEMATICA
| NextPrim[ n_ ] := Block[ {k = n + 1}, While[ !PrimeQ[ k ], k++ ]; k ]; Select[ Range[ 260 ], #*NextPrim[ (# - 1)! ] - NextPrim[ #! ] < 0 & ] (from Robert G. Wilson v)
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CROSSREFS
| Cf. A090661, A089014.
Equals A002981 + 1.
Sequence in context: A000207 A002986 A147569 * A000208 A079154 A101716
Adjacent sequences: A090657 A090658 A090659 * A090661 A090662 A090663
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KEYWORD
| nonn
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AUTHOR
| Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Dec 15 2003
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EXTENSIONS
| Better description from Don Reble, Dec 20, 2003
Three more terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 20 2003
a(14) from Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Jan 05 2004
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