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 A090815 a(n)=denominator(B(2*prime(n))) where prime(n)=n-th prime and B(k) denotes the k-th Bernoulli number. 1
 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; text; internal format)
 OFFSET 1,1 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 LINKS Enrique Pérez Herrero, Table of n, a(n) for n = 1..2000 MATHEMATICA A090815[n_]:=If[!PrimeQ[2*Prime[n]+1], 6, 6*(2*Prime[n]+1)]; Array[A090815, 100] (* Enrique Pérez Herrero, Aug 17 2011 *) PROG (PARI) a(n)=denominator(bernfrac(2*prime(n))) CROSSREFS Cf. A005384. Sequence in context: A179945 A136152 A244066 * A238367 A225228 A336568 Adjacent sequences: A090812 A090813 A090814 * A090816 A090817 A090818 KEYWORD nonn AUTHOR Benoit Cloitre, Feb 11 2004 STATUS approved

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Last modified April 17 02:52 EDT 2024. Contains 371756 sequences. (Running on oeis4.)