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A090815
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a(n)=denominator(B(2*prime(n))) where prime(n)=n-th prime and B(k) denotes the k-th Bernoulli number.
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1
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30, 42, 66, 6, 138, 6, 6, 6, 282, 354, 6, 6, 498, 6, 6, 642, 6, 6, 6, 6, 6, 6, 1002, 1074, 6, 6, 6, 6, 6, 1362, 6, 1578, 6, 6, 6, 6, 6, 6, 6, 2082, 2154, 6, 2298, 6, 6, 6, 6, 6, 6, 6, 2802, 2874, 6, 3018, 6, 6, 6, 6, 6, 3378, 6, 3522, 6, 6, 6, 6, 6, 6, 6, 6, 6, 4314, 6, 6, 6, 6, 6, 6, 6
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| If p and q=2*p+1 are both primes (Sophie Germain primes: A005384) then a(n)=6*q, otherwise a(n)=6 - Enrique Pérez Herrero, Aug 17 2011.
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LINKS
| Enrique Pérez Herrero, Table of n, a(n) for n = 1..2000
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MATHEMATICA
| A090815[n_]:=If[!PrimeQ[2*Prime[n]+1], 6, 6*(2*Prime[n]+1)]; Array[A090815, 100] (* Enrique Pérez Herrero, Aug 17 2011 *)
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PROG
| (PARI) a(n)=denominator(bernfrac(2*prime(n)))
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CROSSREFS
| Cf A005384.
Sequence in context: A175727 A179945 A136152 * A093599 A007304 A160350
Adjacent sequences: A090812 A090813 A090814 * A090816 A090817 A090818
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KEYWORD
| nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), Feb 11 2004
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