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 A367040 #13 Nov 03 2023 11:20:15 %S A367040 1,1,4,15,70,360,1953,11008,63837,378390,2282205,13960890,86411232, %T A367040 540166219,3405341160,21625820793,138216775785,888371346825, %U A367040 5738510504979,37234351046835,242567430368298,1585979835198675,10403866383915844,68453912880893025 %N A367040 G.f. satisfies A(x) = 1 + x^2 + x*A(x)^3. %F A367040 a(n) = Sum_{k=0..floor(n/2)} binomial(2*(n-2*k)+1,k) * binomial(3*(n-2*k),n-2*k)/(2*(n-2*k)+1). %o A367040 (PARI) a(n) = sum(k=0, n\2, binomial(2*(n-2*k)+1, k)*binomial(3*(n-2*k), n-2*k)/(2*(n-2*k)+1)); %Y A367040 Cf. A176697, A367041. %Y A367040 Cf. A366266, A366676. %Y A367040 Cf. A002293, A104979, A186997, A255673, A361245, A364474, A364475, A364478. %K A367040 nonn %O A367040 0,3 %A A367040 _Seiichi Manyama_, Nov 03 2023