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 A176289 Denominators of the rational sequence with e.g.f. (x/2)*(1+exp(-x))/(1-exp(-x)). 7
 1, 1, 6, 1, 30, 1, 42, 1, 30, 1, 66, 1, 2730, 1, 6, 1, 510, 1, 798, 1, 330, 1, 138, 1, 2730, 1, 6, 1, 870, 1, 14322, 1, 510, 1, 6, 1, 1919190, 1, 6, 1, 13530, 1, 1806, 1, 690, 1, 282, 1, 46410, 1, 66, 1, 1590, 1, 798, 1, 870, 1, 354, 1, 56786730, 1, 6, 1, 510 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Denominator of the Bernoulli number B_n, except a(1)=1. A minor variant of the Bernoulli denominators A027642. The series of fractions A164555(n)/A027642(n) =1/1, 1/2, 1/6, 0/1, -1/30,... and the series of fractions A027641(n)/A027642(n) = B_n = 1/1, -1/2, 1/6, 0/1, -1/30.. differ only (by a sign) at n=1. The arithmetic mean of both series is 1/1, 0/1, 1/6, 0/1, -1/30,... , equal to the aerated series A000367(n)/A002445(n). The definition here provides the denominators of this series of arithmetic means. LINKS Antti Karttunen, Table of n, a(n) for n = 0..4096 FORMULA a(2*n) = A002445(n), a(2*n+1)=1. a(n) = A027642(n) for n <> 1. MAPLE seq(denom((bernoulli(i, 0)+bernoulli(i, 1))/2), i=0..64); # Peter Luschny, Jun 17 2012 MATHEMATICA Join[{1, 1}, Rest[Denominator[BernoulliB[Range[80]]]]] (* Harvey P. Dale, Jun 18 2012 *) PROG (PARI) apply(deniominator, Vec(serlaplace((x/2)*(1+exp(-x))/(1-exp(-x))))) \\ Charles R Greathouse IV, Sep 26 2017 (PARI) A176289(n) = if(1==n, n, denominator(bernfrac(n))); \\ Antti Karttunen, Dec 19 2018 CROSSREFS Cf. A027641, A027642, A164555, A176327 (numerators), A141056. Sequence in context: A147327 A145629 A193633 * A118933 A046212 A120105 Adjacent sequences:  A176286 A176287 A176288 * A176290 A176291 A176292 KEYWORD nonn,frac AUTHOR Paul Curtz, Apr 14 2010 EXTENSIONS More terms from Harvey P. Dale, May 03 2012 New name from Peter Luschny, Jun 18 2012 STATUS approved

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Last modified October 17 04:02 EDT 2019. Contains 328106 sequences. (Running on oeis4.)