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 A015033 #15 Sep 08 2022 08:44:39
%S A015033 1,1,10,847,627382,4138659802,244829520301060,130191700295480695111,
%T A015033 622829375926755523108996006,26812578369717035183629988539429726,
%U A015033 10387976772168532331015929118843873280496300
%N A015033 q-Catalan numbers (binomial version) for q=3.
%H A015033 G. C. Greubel, <a href="/A015033/b015033.txt">Table of n, a(n) for n = 0..46</a>
%F A015033 a(n) = binomial(2*n, n, q)/(n+1)_q, where binomial(n,m,q) is the q-binomial coefficient, with q=3.
%F A015033 a(n) = ((1-q)/(1-q^(n+1)))*Product_{k=0..(n-1)} (1-q^(2*n-k))/(1-q^(k+1)), with q=3. - _G. C. Greubel_, Nov 11 2018
%t A015033 Table[2 QBinomial[2n, n, 3]/(3^(n+1) - 1), {n, 0, 20}]
%o A015033 (PARI) q=3; for(n=0, 20, print1(((1-q)/(1-q^(n+1)))*prod(k=0,n-1, (1-q^(2*n-k))/(1-q^(k+1))), ", ")) \\ _G. C. Greubel_, Nov 11 2018
%o A015033 (Magma) q:=3; [1] cat [((1-q)/(1-q^(n+1)))*(&*[(1-q^(2*n-k))/(1-q^(k+1)): k in [0..n-1]]): n in [1..20]]; // _G. C. Greubel_, Nov 11 2018
%Y A015033 Cf. A015030 (q=2).
%K A015033 nonn,easy
%O A015033 0,3
%A A015033 _Olivier Gérard_