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A049421
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Composite numbers n such that (n!/n#)-1 is prime, where n# = primorial numbers A034386.
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3
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4, 6, 8, 16, 21, 34, 39, 45, 50, 72, 76, 133, 164, 202, 216, 221, 280, 496, 605, 2532, 2967, 3337, 8711, 10977, 13724, 15250, 18160, 20943, 33684, 41400
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OFFSET
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1,1
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COMMENTS
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n!/n# is known as n compositorial.
Subset of A140293. Prime numbers are excluded since n!/n# = (n-1)!/(n-1)# when n is prime. - Giovanni Resta, Mar 28 2013
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LINKS
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MATHEMATICA
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Primorial[n_] := Product[Prime[i], {i, 1, PrimePi[n]}];
Select[Range[2,
1000], ! PrimeQ[#] && PrimeQ[(#! / Primorial[#]) - 1] &] (* Robert Price, Oct 11 2019 *)
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CROSSREFS
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KEYWORD
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hard,nonn
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AUTHOR
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Paul Jobling (paul.jobling(AT)whitecross.com)
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EXTENSIONS
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a(27)-a(28) from Daniel Heuer, ca Aug 2000
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STATUS
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approved
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