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 A024488 #12 Jul 02 2025 16:01:55
%S A024488 3,18,210,3150,54054,1009008,19953648,411543990,8764362750,
%T A024488 191413682460,4266468608220,96706621786320,2223107844022800,
%U A024488 51721284534408000,1215794995122150720,28837137540553512390
%N A024488 a(n) = (1/(3n-1))*M(3n; n,n,n), where M(...) is a multinomial coefficient.
%F A024488 a(n) ~ 3^(3*n-1/2) / (2*Pi*n^2). - _Vaclav Kotesovec_, Feb 19 2015
%F A024488 a(n) = A006480(n)/(3*n-1) = 3*A024489(n). - _R. J. Mathar_, Apr 27 2020
%F A024488 D-finite with recurrence: n^2*a(n) -3*(3*n-2)*(3*n-4)*a(n-1)=0. - _R. J. Mathar_, Apr 27 2020
%t A024488 Table[Multinomial[n,n,n]/(3*n-1),{n,1,20}] (* _Vaclav Kotesovec_, Feb 19 2015 *)
%K A024488 nonn,easy
%O A024488 1,1
%A A024488 _Clark Kimberling_
%E A024488 More terms from _James Sellers_, Aug 08 2000