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 A137970 #10 Mar 03 2018 13:53:45
%S A137970 1,1,6,33,236,1776,14148,117070,995568,8653068,76508562,686035674,
%T A137970 6223653276,57018806567,526802616954,4902775644477,45919926029588,
%U A137970 432511043009679,4094087001128088,38927025591433926,371607779425490280
%N A137970 G.f. satisfies A(x) = 1 + x*(1 + x*A(x)^3)^6.
%H A137970 Vaclav Kotesovec, <a href="/A137970/b137970.txt">Table of n, a(n) for n = 0..350</a>
%F A137970 G.f.: A(x) = 1 + x*B(x)^6 where B(x) is the g.f. of A137969.
%F A137970 a(n) = Sum_{k=0..n-1} C(6*(n-k),k)/(n-k) * C(3*k,n-k-1) for n>0 with a(0)=1. - _Paul D. Hanna_, Jun 16 2009
%F A137970 a(n) ~ sqrt(6*s*(1-s)*(3-4*s) / ((102*s - 72)*Pi)) / (n^(3/2) * r^n), where r = 0.0971328555591006631243189792661187629516513365080... and s = 1.377827066365760014851094517875193622070040930150... are real roots of the system of equations s = 1 + r*(1 + r*s^3)^6, 18 * r^2 * s^2 * (1 + r*s^3)^5 = 1. - _Vaclav Kotesovec_, Nov 22 2017
%o A137970 (PARI) {a(n)=local(A=1+x*O(x^n));for(i=0,n,A=1+x*(1+x*A^3)^6);polcoeff(A,n)}
%o A137970 (PARI) a(n)=if(n==0,1,sum(k=0,n-1,binomial(6*(n-k),k)/(n-k)*binomial(3*k,n-k-1))) \\ _Paul D. Hanna_, Jun 16 2009
%Y A137970 Cf. A137969, A137971; A137968, A137972, A137974.
%K A137970 nonn
%O A137970 0,3
%A A137970 _Paul D. Hanna_, Feb 26 2008