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 A113409 #10 Nov 27 2017 12:22:52
%S A113409 1,1,2,3,6,11,21,39,74,141,271,521,1004,1939,3756,7291,14176,27599,
%T A113409 53805,105031,205268,401573,786328,1541037,3022528,5932657,11652617,
%U A113409 22901865,45037432,88616807,174454943,343606183,677074350,1334744305
%N A113409 A transform of the central binomial coefficients A001405.
%C A113409 Row sums of A113408.
%H A113409 G. C. Greubel, <a href="/A113409/b113409.txt">Table of n, a(n) for n = 0..1000</a>
%F A113409 G.f.: (1-xc(x^2))/(1-x^2-x^4c(x^4)), where c(x) is the g.f. of A000108.
%F A113409 a(n) = Sum_{k=0..floor(n/2)} C(n-k, k)*C(k, floor(k/2)).
%F A113409 a(n) = Sum_{k=0..n} C((n+k)/2, k)*C(floor((n-k)/2), floor((n-k)/4)).
%F A113409 Conjecture: (n+2)*a(n)-2*(n+1)*a(n-1) +(n-4)*a(n-2) +2*a(n-3) +4*(2-n)*a(n-4)=0. - _R. J. Mathar_, Nov 07 2012
%F A113409 a(n) ~ 2^(n + 3/2) / sqrt(3*Pi*n). - _Vaclav Kotesovec_, Nov 27 2017
%t A113409 Table[Sum[Binomial[n - k, k]*Binomial[k, Floor[k/2]], {k, 0, Floor[n/2]}], {n,0,50}] (* _G. C. Greubel_, Mar 09 2017 *)
%o A113409 (PARI) for(n=0,25, print1(sum(k=0,floor(n/2), binomial(n-k,k)*binomial(k,floor(k/2))), ", ")) \\ _G. C. Greubel_, Mar 09 2017
%K A113409 easy,nonn
%O A113409 0,3
%A A113409 _Paul Barry_, Oct 28 2005