%I #14 Dec 21 2015 14:09:04
%S 4,8,32,96,1536,960,184320,161280,8257536,2903040,14863564800,
%T 638668800,1569592442880,49816166400,5713316492083200,83691159552000,
%U 1096956766479974400,2845499424768000,6713375410857443328000
%N Denominator of S(n)/Pi^n, where S(n) = Sum((4k+1)^(-n),k,-inf,+inf).
%H N. D. Elkies, <a href="http://arXiv.org/abs/math.CA/0101168">On the sums Sum((4k+1)^(-n),k,-inf,+inf)</a>, arXiv:math/0101168 [math.CA], 2001-2003.
%H N. D. Elkies, <a href="http://www.jstor.org/stable/3647742">On the sums Sum_{k = -infinity .. infinity} (4k+1)^(-n)</a>, Amer. Math. Monthly, 110 (No. 7, 2003), 561-573.
%F There is a simple formula in terms of Euler and Bernoulli numbers.
%e The first few values of S(n)/Pi^n are 1/4, 1/8, 1/32, 1/96, 5/1536, 1/960, ...
%t s[n_?EvenQ] := (-1)^(n/2-1)*(2^n-1)*BernoulliB[n]/(2*n!); s[n_?OddQ] := (-1)^((n-1)/2)*2^(-n-1)*EulerE[n-1]/(n-1)!; Table[s[n] // Denominator, {n, 1, 19}] (* _Jean-François Alcover_, May 13 2013 *)
%t a[n_] := Sum[((-1)^k/(2*k+1))^n, {k, 0, Infinity}] /. Pi -> 1 // Denominator; Table[a[n], {n, 1, 19}] (* _Jean-François Alcover_, Jun 20 2014 *)
%Y Numerators: A050970.
%K nonn,frac
%O 1,1
%A _N. J. A. Sloane_, Mar 24 2002
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