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A139056
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Numbers k for which (k!-3)/3 is prime.
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56
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4, 6, 12, 16, 29, 34, 43, 111, 137, 181, 528, 2685, 39477, 43697
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OFFSET
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1,1
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COMMENTS
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Corresponding primes (k!-3)/3 are in A139057.
a(13) > 10000. The PFGW program has been used to certify all the terms up to a(12), using a deterministic test which exploits the factorization of a(n) + 1. - Giovanni Resta, Mar 28 2014
98166 is a member of the sequence but its index is not yet determined. The interval where sieving and tests were not run is [60000,90000]. - Serge Batalov, Feb 24 2015
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LINKS
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MATHEMATICA
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a = {}; Do[If[PrimeQ[(-3 + n!)/3], AppendTo[a, n]], {n, 1, 1000}]; a
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PROG
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(PARI) for(n=1, 1000, if(floor(n!/3-1)==n!/3-1, if(ispseudoprime(n!/3-1), print(n)))) \\ Derek Orr, Mar 28 2014
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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Definition corrected by Derek Orr, Mar 28 2014
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STATUS
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approved
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