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 A349819 #9 Feb 28 2023 17:04:11 %S A349819 3,1,3,4,20,31,182,304,1932,3364,22407,40044,275132,500522,3515564, %T A349819 6478784,46260604,86094668,622636764,1167752848,8531618640, %U A349819 16100882359,118615471982,225001039696,1669094344820,3179713880524,23725950404610,45364387834120,340192536782760 %N A349819 Central column (ignoring the zeros) of A349813, or leading entries in rows of A349814. %H A349819 Andrew Howroyd, <a href="/A349819/b349819.txt">Table of n, a(n) for n = 0..500</a> %F A349819 a(n) = [x^floor(3*n/2+1)](-3 - x + x^2 + 3*x^3)*(1 + x + x^2 + x^3)^(n-1) for n > 0. - _Andrew Howroyd_, Feb 28 2023 %o A349819 (PARI) a(n) = if(n==0, 3, polcoef((-3 - x + x^2 + 3*x^3)*(1 + x + x^2 + x^3)^(n-1), 3*n\2+1)) \\ _Andrew Howroyd_, Feb 28 2023 %Y A349819 Cf. A349813, A349814. %K A349819 nonn %O A349819 0,1 %A A349819 _N. J. A. Sloane_, Dec 24 2021 %E A349819 Offset corrected and terms a(21) and beyond from _Andrew Howroyd_, Feb 28 2023