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A051888
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a(n) is the smallest prime p such that p*n! + 1 is prime.
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7
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2, 2, 2, 2, 3, 2, 3, 3, 7, 3, 3, 5, 2, 3, 13, 7, 31, 5, 2, 7, 17, 67, 41, 3, 13, 3, 43, 17, 97, 7, 29, 109, 3, 71, 5, 2, 7, 41, 3, 59, 3, 11, 29, 7, 107, 67, 79, 3, 743, 149, 163, 2, 211, 2, 19, 71, 73, 23, 37, 113, 149, 67, 41, 617, 107, 37, 107, 283, 113, 19, 239, 107, 73, 97, 5
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OFFSET
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0,1
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COMMENTS
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The PFGW program has been used to certify all the primes corresponding to the terms up to a(1000), using a deterministic test which exploits the factorization of a(n) - 1. - Giovanni Resta, May 30 2018
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LINKS
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FORMULA
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MATHEMATICA
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Do[k = 1; While[ !PrimeQ[ Prime[k]*n! + 1], k++ ]; Print[ Prime[k]], {n, 1, 75} ]
spp[n_]:=Module[{p=2, nf=n!}, While[!PrimeQ[p*nf+1], p=NextPrime[p]]; p]; Array[ spp, 80, 0] (* Harvey P. Dale, May 17 2019 *)
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PROG
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(PARI) a(n) = {my(p=2); while (!isprime(p*n! + 1), p = nextprime(p+1)); p; } \\ Michel Marcus, May 28 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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