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 A354657 #6 Jun 04 2022 08:01:24
%S A354657 1,9,49,210,765,2492,7434,20700,54420,136360,327789,760102,1707342,
%T A354657 3728025,7935525,16507152,33624045,67186077,131891825,254710260,
%U A354657 484474753,908538081,1681364124,3073166600,5551851375,9919925145,17541289017,30714092066,53279031420
%N A354657 a(n) = A354655(n)/3, for n >= 1.
%H A354657 Paul D. Hanna, <a href="/A354657/b354657.txt">Table of n, a(n) for n = 1..100</a>
%F A354657 a(n) = A354655(n)/3, for n >= 1.
%F A354657 a(n) = A354650(n,2)/3, for n >= 1.
%F A354657 a(n) = (-1)^(n+1) * A354649(n,2)/3, for n >= 1.
%o A354657 (PARI) {A354650(n,k) = my(A=[1+y]); for(i=1,n, A = concat(A,0);
%o A354657 A[#A] = polcoeff(y + sum(m=0,sqrtint(2*#A+9), (-1)^m * x^(m*(m-1)/2) * (1 - x^(2*m+1)) * Ser(A)^(m*(m+1)/2) ),#A-1) );
%o A354657 polcoeff(A[n+1],k,y)}
%o A354657 for(n=1,30,print1(A354650(n,2)/3,", "))
%Y A354657 Cf. A354649, A354650, A354655.
%K A354657 nonn
%O A354657 1,2
%A A354657 _Paul D. Hanna_, Jun 02 2022