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 A193198 #15 Jul 02 2022 09:27:49
%S A193198 1,1,4,28,352,7696,296704,19845568,2325071872,472050401536,
%T A193198 167325747134464,102717666720160768,109887628080679616512,
%U A193198 203517277347030338768896,656102983404750860283019264,3660938644168893995628877692928
%N A193198 G.f.: A(x) = Sum_{n>=0} x^n/(1 - 3^n*x)^n.
%H A193198 Seiichi Manyama, <a href="/A193198/b193198.txt">Table of n, a(n) for n = 0..90</a>
%F A193198 a(n) = Sum_{k=0..n-1} binomial(n-1,k)*3^(k*(n-k)) for n>0 with a(0)=1.
%e A193198 G.f.: A(x) = 1 + x + 4*x^2 + 28*x^3 + 352*x^4 + 7696*x^5 +...
%e A193198 where:
%e A193198 A(x) = 1 + x/(1-3*x) + x^2/(1-9*x)^2 + x^3/(1-27*x)^3 + x^4/(1-81*x)^4 +...
%o A193198 (PARI) {a(n)=local(A=1);A=1+sum(m=1,n,x^m/(1-3^m*x +x*O(x^n))^m);polcoeff(A,n)}
%o A193198 (PARI) {a(n)=if(n==0,1,sum(k=0,n-1,binomial(n-1,k)*3^(k*(n-k))))}
%Y A193198 Cf. A000684, A135079, A193199.
%K A193198 nonn
%O A193198 0,3
%A A193198 _Paul D. Hanna_, Jul 17 2011