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 A247256 #14 Nov 30 2014 04:13:06
%S A247256 1,1,0,-6,-12,20,300,252,-3024,-36720,106560,110880,12212640,
%T A247256 -125629920,1005286464,-16865735040,252900345600,-3575747185920,
%U A247256 58447092395520,-1014901444454400,18218754479923200,-346655486035998720,6952232946445839360,-145913061049673702400,3205301440394904238080
%N A247256 Exponential generating function = (1+x)^(1-x^2).
%F A247256 a(n) ~ 2 * (-1)^n * n! / n^2 * (1 + 4*log(n)/n). - _Vaclav Kotesovec_, Nov 30 2014
%e A247256 (1+x)^(1-x^2) = 1 + x - x^3 - 1/2*x^4 + 1/6*x^5 + 5/12*x^6 + 1/20*x^7 - 3/40*x^8 - 17/168*x^9 + 37/1260*x^10 + 1/360*x^11 + 257/10080*x^12 - ...
%t A247256 CoefficientList[Series[(1+x)^(1-x^2), {x, 0, 20}], x] * Range[0, 20]! (* _Vaclav Kotesovec_, Nov 30 2014 *)
%o A247256 (PARI) Vec(serlaplace((1+x+O(x^25))^(1-x^2)))
%Y A247256 Cf. A005727, A007120, A247212.
%K A247256 sign
%O A247256 0,4
%A A247256 _Franklin T. Adams-Watters_, Nov 29 2014