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 A134780 #3 Mar 30 2012 18:37:07
%S A134780 1,2,1,2,1,3,-1,6,-7,19,-33,73,-146,311,-652,1392,-2977,6420,-13899,
%T A134780 30247,-66078,144911,-318853,703768,-1557718,3456813,-7689531,
%U A134780 17142887,-38296408,85715645,-192191445,431647744,-970958480,2187288804,-4934101775,11144794835,-25203825094
%N A134780 The square root of A134779.
%t A134780 a[n_] := a[n] = Block[{k = a[n - 1] + 2, s = Sum[ a[i]*x^i, {i, 0, n - 1}]}, If[IntegerQ@ Last@ CoefficientList[ Series[ Sqrt[s + k*x^n], {x, 0, n}], x], k, k + 1]]; a[0] = 1; CoefficientList[ Series[ Sqrt[ Sum[ a[i]*x^i, {i, 0, 36}]], {x, 0, 36}], x]
%Y A134780 Cf. A084202, A134779.
%K A134780 sign
%O A134780 0,2
%A A134780 _Paul D. Hanna_ & _Robert G. Wilson v_, Nov 11 2007