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 A054131 #11 May 30 2022 08:24:34
%S A054131 2,5,24,134,802,4960,31212,198504,1271754,8192780,53009614,344213930,
%T A054131 2241814696,14637778784,95786210880
%N A054131 T(2n,n), array T as in A054126.
%F A054131 a(n) = A052509(4*n,3*n+1) + A052509(4*n,n) = 2^(n-1) + Sum_{m=0..n} binomial(3*n,m). for n >= 1. - _Jianing Song_, May 30 2022
%o A054131 (PARI) a(n) = if(n==0, 2, 2^(n-1) + sum(m=0, n, binomial(3*n,m))) \\ _Jianing Song_, May 30 2022
%Y A054131 Cf. A054126.
%K A054131 nonn
%O A054131 0,1
%A A054131 _Clark Kimberling_