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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
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.
MATHEMATICA
NextPrim[ n_ ] := Block[ {k = n + 1}, While[ !PrimeQ[ k ], k++ ]; k ]; Select[ Range[ 260 ], #*NextPrim[ (# - 1)! ] - NextPrim[ #! ] < 0 & ] (* Robert G. Wilson v *)
CROSSREFS
Equals A002981 + 1.
Sequence in context: A000207 A002986 A147569 * A288140 A287594 A296271
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