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 A054133 #15 May 30 2022 08:24:51
%S A054133 2,7,39,236,1479,9418,60492,390720,2534115,16489802,107594725,
%T A054133 703681448,4611414244,30273029080,199045400424
%N A054133 T(2n-1,n) where T is the array in A054126.
%F A054133 a(n) = A052509(4*n-2,3*n) + A052509(4*n-2,n-1) = 2^(n-2) + Sum_{m=0..n-1} binomial(3*n-1,m) for n >= 2. - _Jianing Song_, May 30 2022
%o A054133 (PARI) a(n) = if(n==1, 2, 2^(n-2) + sum(m=0, n-1, binomial(3*n-1, m))) \\ _Jianing Song_, May 30 2022
%Y A054133 Cf. A054126.
%K A054133 nonn,more
%O A054133 1,1
%A A054133 _Clark Kimberling_
%E A054133 Definition clarified by _Eric Rowland_, May 29 2022