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 A002803 M4980 N2140 #30 May 09 2021 06:08:09
%S A002803 1,15,140,1050,6930,42042,240240,1312740,6928350,35565530,178474296,
%T A002803 878850700,4259045700,20359174500,96172862400,449608131720,
%U A002803 2082743551350,9569730173850,43651400793000,197809768856700
%N A002803 a(n) = (2n+4)!/(4!*n!*(n+1)!).
%D A002803 C. Jordan, Calculus of Finite Differences. Budapest, 1939, p. 449.
%D A002803 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A002803 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A002803 T. D. Noe, <a href="/A002803/b002803.txt">Table of n, a(n) for n = 0..200</a>
%H A002803 T. R. S. Walsh and A. B. Lehman, <a href="http://dx.doi.org/10.1016/0095-8956(75)90050-7">Counting rooted maps by genus. III: Nonseparable maps</a>, J. Combinatorial Theory Ser. B 18 (1975), 222-259.
%F A002803 G.f.: 2F1(5/2,3;2;4x) =(1+x)/(1-4x)^(7/2). - _R. J. Mathar_, Aug 09 2015
%F A002803 a(n) = A020918(n)+A020918(n-1). - _R. J. Mathar_, Aug 09 2015
%F A002803 D-finite with recurrence n*(n+1)*a(n) -2*(n+2)*(2*n+3)*a(n-1)=0. - _R. J. Mathar_, Feb 08 2021
%t A002803 Table[(2*n+4)!/(4!*n!*(n+1)!), {n, 0, 20}] (* _Vladimir Joseph Stephan Orlovsky_, Dec 13 2008 *)
%Y A002803 Cf. A020918.
%K A002803 nonn,easy
%O A002803 0,2
%A A002803 _N. J. A. Sloane_