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 A106469 #11 Feb 06 2024 11:57:44
%S A106469 1,2,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,
%T A106469 2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,
%U A106469 2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4
%N A106469 Expansion of (1 + x^2)*(1 + 2*x)/(1 - x^2).
%H A106469 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,1).
%F A106469 a(0)=1, a(n)=(2-0^((n-1)/2))(1-(-1)^n)+(2-0^(n/2))(1+(-1)^n)/2, n>1.
%t A106469 CoefficientList[Series[(1+x^2)(1+2x)/(1-x^2),{x,0,95}],x] (* _James C. McMahon_, Feb 02 2024 *)
%Y A106469 Row sums of A106468.
%K A106469 easy,nonn
%O A106469 0,2
%A A106469 _Paul Barry_, May 03 2005