This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A230265 #5 Oct 15 2013 10:56:45 %S A230265 2,12,720,30240,1209600,6842880,1307674368000,74724249600, %T A230265 1524374691840000,5109094217170944000,802857662698291200000, %U A230265 287777551824322560000,1693824136731743669452800000,186134520519971831808000000 %N A230265 Denominators of eta(2*n)/Pi^(2*n), where eta(n) is the Dirichlet eta function. %C A230265 The first 5 terms of this sequence are the same as in A060055. %H A230265 Wikipedia, <a href="http://en.wikipedia.org/wiki/Dirichlet_eta_function">Dirichlet eta function</a> %H A230265 Index entries for <a href="/index/Be#Bernoulli">Bernoulli numbers</a> B(2n) %F A230265 a(n) = A036280(n)*Pi^(2*n)/(zeta(2*n)*(1 - 2^(1-2*n))). %F A230265 a(n) = denominator((-1)^(n+1)*BernoulliB(2*n)*(2^(2*n-1) - 1)/(2*n)!). %F A230265 a(n) = 2*A036281(n). %o A230265 (PARI) for(n=0, 7, print1(2*denominator(polcoeff(Ser(1/sin(x)), 2*n-1)), ", ")); %Y A230265 Numerators give A036280. %K A230265 nonn,easy,frac %O A230265 0,1 %A A230265 _Arkadiusz Wesolowski_, Oct 14 2013