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 A228901 #6 May 26 2025 23:50:53
%S A228901 1,3,15,155,2685,65517,2063205,79715229,3653521179,193876702019,
%T A228901 11696128639195,790788563411431,59238930606369007,4870881096635599567,
%U A228901 436176889680415116607,42256722956163045301807,4403938204071514872757477,491317594015782152377769725,58423874601431980415156917525
%N A228901 Column 1 of triangle A228900.
%C A228901 Triangle A228900 is defined by g.f.: exp( Sum_{n>=1} x^n/n * Sum_{k=0..n} binomial(n^2, (n-k)*k) * y^k ).
%o A228901 (PARI) {a(n)=polcoeff(polcoeff(exp(sum(m=1, n, x^m/m*sum(j=0, m, binomial(m^2, (m-j)*j)*y^j))+x*O(x^n)), n, x), 1, y)}
%o A228901 for(n=1, 20, print1(a(n), ", "))
%Y A228901 Cf. A228900.
%K A228901 nonn
%O A228901 1,2
%A A228901 _Paul D. Hanna_, Sep 07 2013