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 A128056 #5 Jun 27 2013 09:57:17 %S A128056 1,-3,-6,28,56,-288,-576,3008,6016,-31488,-62976,329728,659456, %T A128056 -3452928,-6905856,36159488,72318976,-378667008,-757334016,3965452288, %U A128056 7930904576,-41526755328,-83053510656,434873827328 %N A128056 Hankel transform of A128057. %C A128056 a(n)=2^A128054(n)*A128053(n). Hankel transform of A128058. %F A128056 a(n)=A128055(n)*((cos(pi*n/2)-sin(pi*n/2))((F(n-1)+F(n+1))(5/6-cos(pi*n/3)/3)(1+(-1)^n)/2 +(F(n)+F(n+2))(5/6-cos(pi*(n+1)/3)/3)(1-(-1)^n)/2)). %F A128056 Empirical g.f.: -(2*x-1)*(4*x^2-x+1) / (16*x^4+12*x^2+1). - _Colin Barker_, Jun 27 2013 %K A128056 easy,sign %O A128056 0,2 %A A128056 _Paul Barry_, Feb 13 2007