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 A110525 #6 Aug 30 2017 01:41:30
%S A110525 1,0,1,3,19,141,1180,10593,99712,971067,9702388,98899638,1024429861,
%T A110525 10752006033,114097140757,1222113460332,13195550763793,
%U A110525 143470913825427,1569448022488435,17261100136608984,190752895126918819
%N A110525 Expansion of 1/(1-x^2*c(3x)), c(x) the g.f. A000108.
%C A110525 Diagonal sums of A110518.
%H A110525 G. C. Greubel, <a href="/A110525/b110525.txt">Table of n, a(n) for n = 0..930</a>
%F A110525 a(n) = Sum_{k=0..floor(n/2)} (k/(n-k))*C(2*n-3*k-1, n-2*k)*3^(n-2*k).
%t A110525 Join[{1}, Table[Sum[(k/(n - k))*Binomial[2*n - 3*k - 1, n - 2*k]*3^(n - 2*k), {k, 0, Floor[n/2]}], {n, 1, 50}]] (* _G. C. Greubel_, Aug 30 2017 *)
%o A110525 (PARI) concat([1], for(n=1,25, print1(sum(k=0,n\2, (k/(n - k))*binomial(2*n - 3*k - 1, n - 2*k)*3^(n - 2*k)), ", "))) \\ _G. C. Greubel_, Aug 30 2017
%K A110525 easy,nonn
%O A110525 0,4
%A A110525 _Paul Barry_, Jul 24 2005