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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
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.)