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 A113283 #5 Oct 18 2020 06:59:11
%S A113283 1,3,11,51,255,1325,7039,37951,206799,1135969,6279509,34889553,
%T A113283 194664283,1089943229,6120967411,34463104999,194474062663,
%U A113283 1099571123853,6227893795649,35329149864161,200691916063033,1141489886332555
%N A113283 Even bisection of A113281: a(n) = A113281(2*n).
%F A113283 G.f.: ( (1+x)/(1-x)/(1-6*x+x^2)*(1-x+(1-6*x+x^2)^(1/2))/2 )^(1/2).
%F A113283 a(n) ~ (1 + sqrt(2))^(2*n + 1/2) / (2*sqrt(Pi*n)). - _Vaclav Kotesovec_, Oct 18 2020
%o A113283 (PARI) {a(n)=local(x=X+X*O(X^n));polcoeff( ((1+x)/(1-x)/(1-6*x+x^2)*(1-x+(1-6*x+x^2)^(1/2))/2)^(1/2),n,X)}
%Y A113283 Cf. A113281, A113282, A113284.
%K A113283 nonn
%O A113283 0,2
%A A113283 _Paul D. Hanna_, Oct 22 2005