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 A113828 #9 Sep 02 2013 03:16:11
%S A113828 1,9,25,57,121,633,1657,3705,7801,40569,106105,237177,499321,2596473,
%T A113828 6790777,15179385,31956601,166174329,434609785,971480697,2045222521,
%U A113828 10635157113,27815026297,62174764665,130894241401,680650055289
%N A113828 a(n) = Sum[2^(A047260(i)-1), {i,1,n}].
%F A113828 Empirical g.f.: x*(32*x^3+16*x^2+8*x+1) / ((x-1)*(8*x^2-1)*(8*x^2+1)). - _Colin Barker_, Sep 01 2013
%e A113828 a(2) = 2^(A047260(1)-1) + 2^(A047260(2)-1) = 2^0 + 2^3 = 9
%t A113828 a = {}; s = 0; For[n = 1, n < 41, n++, If[Length[Intersection[{Mod[n, 6]}, {0, 1, 4, 5}]] > 0, s = s + 2^(n - 1); AppendTo[a, s]]]; a
%Y A113828 Cf. A047260.
%K A113828 nonn,less
%O A113828 1,2
%A A113828 _Artur Jasinski_, Jan 27 2006
%E A113828 Edited by _Stefan Steinerberger_, Jul 23 2007