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 A131298 #15 Jun 25 2023 03:44:43
%S A131298 1,1,2,4,6,11,18,30,50,82,135,221,361,589,959,1560,2535,4116,6679,
%T A131298 10832,17560,28457,46103,74674,120928,195802,316995,513148,830608,
%U A131298 1344372,2175796,3521249,5698477
%N A131298 Diagonal sums of A104730.
%H A131298 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,2,0,-2,-1).
%F A131298 G.f.: (1-x^2)/((1-x-x^2)*(1-x^2-x^3)) = (1+x)/(1-x-x^2) - x*(1+x)/(1-x^2-x^3).
%F A131298 a(n) = Sum_{k=0..floor(n/2)} C(n-k+1,k) - C(k,n-2k+1).
%t A131298 LinearRecurrence[{1,2,0,-2,-1},{1,1,2,4,6},40] (* _Harvey P. Dale_, Aug 21 2021 *)
%Y A131298 Cf. A104730.
%K A131298 easy,nonn
%O A131298 0,3
%A A131298 _Paul Barry_, Jun 26 2007