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 A101480 #7 Aug 22 2012 12:06:41
%S A101480 0,1,3,3,3,11,63,43,-837,171,34023,683,-1800477,2731,132912783,10923,
%T A101480 -12927652917,43691,1603253204343,174763,-246914125142157,699051,
%U A101480 46232582930156703,2796203,-10343022775699132197,11184811,2724715006195438297863,44739243,-834839760935753154167037
%N A101480 E.g.f. (1/cosh(x)+tanh(x))*(exp(2*x)-exp(-x))/3.
%C A101480 A transform of the Jacobsthal numbers.
%C A101480 a(2n)=A007583(n)=(2*4^n+1)/3.
%t A101480 With[{nn=30},CoefficientList[Series[(1/Cosh[x]+Tanh[x]) (Exp[2x]- Exp[-x])/3, {x,0,nn}],x]Range[0,nn]!] (* _Harvey P. Dale_, Aug 22 2012 *)
%Y A101480 Cf. A101473, A001045.
%K A101480 easy,sign
%O A101480 0,3
%A A101480 _Paul Barry_, Jan 21 2005
%E A101480 Corrected by _N. J. A. Sloane_, Nov 05 2005