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 A349818 #10 Feb 28 2023 17:04:16 %S A349818 1,1,1,2,8,13,74,124,784,1364,9069,16194,111144,202070,1418196, %T A349818 2612376,18642208,34682348,250706548,470066728,3433030048,6477333149, %U A349818 47703926354,90472092748,670963514192,1278016171132,9534032792470,18226719157820,136658371126320 %N A349818 Central column (ignoring the zeros) of A349815, or leading entries in rows of A349816. %C A349818 Note that the analogous sequence for A349812 is the Motzkin numbers A001006. %H A349818 Andrew Howroyd, <a href="/A349818/b349818.txt">Table of n, a(n) for n = 0..500</a> %F A349818 a(n) = [x^floor(3*n/2+1)](-1 - x + x^2 + 3*x^3)*(1 + x + x^2 + x^3)^(n-1) for n > 0. - _Andrew Howroyd_, Feb 28 2023 %o A349818 (PARI) a(n) = if(n==0, 1, polcoef((-1 - x + x^2 + x^3)*(1 + x + x^2 + x^3)^(n-1), 3*n\2+1)) \\ _Andrew Howroyd_, Feb 28 2023 %Y A349818 Cf. A001006, A349812, A349815, A349816. %K A349818 nonn %O A349818 0,4 %A A349818 _N. J. A. Sloane_, Dec 24 2021 %E A349818 Offset corrected and terms a(21) and beyond from _Andrew Howroyd_, Feb 28 2023