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 A361556 #7 Mar 19 2023 05:01:15
%S A361556 1,5,61,1660,47460,1621116,58002140,2213389940,87301563690,
%T A361556 3555890156445,148125509781095,6292884402884976,271565202254735207,
%U A361556 11878392121526009800,525519782174930309205,23481280252471520720288,1058270749214634093475910,48058678036035725619136698
%N A361556 Central terms of triangle A361550.
%H A361556 Paul D. Hanna, <a href="/A361556/b361556.txt">Table of n, a(n) for n = 0..50</a>
%F A361556 a(n) = A361550(2*n,n) for n >= 0.
%F A361556 a(n) ~ c * d^n / n^2, where d = 51.1751... and c = 0.12624... - _Vaclav Kotesovec_, Mar 19 2023
%o A361556 (PARI) {A361550(n,k) = my(A=[1]); for(i=1, n, A = concat(A, 0);
%o A361556 A[#A] = polcoeff(x*y - prod(m=1, #A, (1 - x^m) * (1 - x^m*Ser(A)) * (1 - x^(m-1)/Ser(A)) * (1 - x^(2*m-1)*Ser(A)^2) * (1 - x^(2*m-1)/Ser(A)^2) ), #A-1) );
%o A361556 polcoeff(polcoeff(Ser(A),n,x),k,y)}
%o A361556 for(n=0, 20, print1(A361550(2*n,n), ", "))
%Y A361556 Cf. A361550.
%K A361556 nonn
%O A361556 0,2
%A A361556 _Paul D. Hanna_, Mar 19 2023