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 A383525 #9 Apr 29 2025 08:54:56
%S A383525 1,1,1,10,33,76,370,1569,5089,20584,88776,336865,1336434,5639869,
%T A383525 22824789,92230285,384930529,1595575648,6570596764,27418859721,
%U A383525 114736740808,478594009281,2005907811469,8437974722463,35480386059826,149466347150701,631299305598625,2668522402478179
%N A383525 a(n) = Sum_{k=0..floor(n/3)} binomial(n,k)^2 * binomial(n-2*k,k).
%C A383525 Diagonal of the rational function 1 / ((1-x)*(1-y)*(1-z) - x*y*z^3).
%o A383525 (PARI) a(n) = sum(k=0, n\3, binomial(n, k)^2*binomial(n-2*k, k));
%Y A383525 Cf. A000172, A248658, A383526.
%K A383525 nonn
%O A383525 0,4
%A A383525 _Seiichi Manyama_, Apr 29 2025