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 A216923 The denominators of Zagier's modification of the Bernoulli numbers. 4
 4, 24, 4, 80, 4, 1260, 4, 1120, 4, 264, 4, 12012, 4, 312, 4, 38080, 4, 1220940, 4, 83600, 4, 552, 4, 78936, 4, 24, 4, 30160, 4, 62300700, 4, 2360960, 4, 24, 4, 430666236, 4, 888, 4, 47986400, 4, 202145580, 4, 79120, 4, 1128, 4, 126139728, 4, 264, 4, 4240, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Israel, Table of n, a(n) for n = 1..4655 M. W. Coffey, V. de Angelis, A. Dixit, V. H. Moll, et al., The Zagier polynomials. Part II: Arithmetic properties of coefficients, arXiv:1303.6590 [math.NT], 2013. Atul Dixit, Victor H. Moll, Christophe Vignat, The Zagier modification of Bernoulli numbers and a polynomial extension. Part I, arXiv:1209.4110v1 [math.NT], 2012. D. Zagier, A modified Bernoulli number, Nieuw Archief voor Wiskunde, 16:63-72, 1998. FORMULA a(n) = denominator(sum_{r=0..n} C(n+r,2*r)*B(r)/(n+r)); B(r) the Bernoulli numbers. a(n)=4 if n is odd. - Robert Israel, Mar 08 2018 MAPLE f:= proc(n) if n::odd then 4 else denom(-n/4 + add(binomial(n+r, 2*r)*bernoulli(r)/(n+r), r=0..n, 2)) fi end proc: map(f, [\$1..100]); # Robert Israel, Mar 08 2018 MATHEMATICA a[n_] := Sum[ Binomial[n + k, 2*k]*BernoulliB[k]/(n + k), {k, 0, n}] // Denominator; Table[a[n], {n, 1, 53}] (* Jean-François Alcover, Jul 26 2013 *) PROG (Sage) def A216923(n):     return add(binomial(n+r, 2*r)*bernoulli(r)/(n+r) for r in (0..n)).denominator() [A216923(n) for n in (1..53)] (PARI) a(n) = denominator(sum(r=0, n, binomial(n+r, 2*r)*bernfrac(r)/(n+r))); \\ Michel Marcus, Aug 05 2018 CROSSREFS Cf. A216922 (numerators). Sequence in context: A319145 A024543 A010294 * A233149 A169688 A222595 Adjacent sequences:  A216920 A216921 A216922 * A216924 A216925 A216926 KEYWORD nonn AUTHOR Peter Luschny, Sep 20 2012 STATUS approved

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Last modified July 31 14:49 EDT 2021. Contains 346374 sequences. (Running on oeis4.)