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 A203231 #8 Oct 15 2013 14:19:18
%S A203231 1,4,15,24,81,108,351,432,1377,1620,5103,5832,18225,20412,63423,69984,
%T A203231 216513,236196,728271,787320,2421009,2598156,7971615,8503056,26040609,
%U A203231 27634932,84499119,89282088,272629233,286978140,875283327,918330048
%N A203231 (n-1)-st elementary symmetric function of the first n terms of the periodic sequence (3,1,3,1,3,1,3,1,...).
%F A203231 Conjecture: a(n) = 6*a(n-2)-9*a(n-4) with G.f. x*(1+4*x+9*x^2) / (-1+3*x^2)^2 . - _R. J. Mathar_, Oct 15 2013
%t A203231 r = {3, 1, 3, 1, 3, 1};
%t A203231 s = Flatten[{r, r, r, r, r, r, r, r, r}];
%t A203231 t[n_] := Part[s, Range[n]]
%t A203231 a[n_] := SymmetricPolynomial[n - 1, t[n]]
%t A203231 Table[a[n], {n, 1, 32}] (* A203231 *)
%Y A203231 Cf. A010684, A203230, A120908 (bisection).
%K A203231 nonn
%O A203231 1,2
%A A203231 _Clark Kimberling_, Dec 30 2011