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 A007681 M4632 #21 Mar 26 2023 10:27:28
%S A007681 1,9,50,294,1944,14520,121680,1134000,11652480,130999680,1600300800,
%T A007681 21115987200,299376000000,4539498163200,73316942899200,
%U A007681 1256675067648000,22784918188032000,435717099417600000
%N A007681 a(n) = (2*n+1)^2*n!.
%D A007681 H. W. Gould, A class of binomial sums and a series transform, Utilitas Math., 45 (1994), 71-83.
%D A007681 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A007681 Delbert L. Johnson, <a href="/A007681/b007681.txt">Table of n, a(n) for n = 0..447</a>
%H A007681 H. W. Gould, <a href="/A007680/a007680.pdf">A class of binomial sums and a series transform</a>, Utilitas Math., 45 (1994), 71-83. (Annotated scanned copy)
%F A007681 E.g.f.: (1 + 6*x + x^2)/(1 - x)^3. - _Ilya Gutkovskiy_, May 12 2017
%t A007681 Table[(2n+1)^2 n!,{n,0,20}] (* _Harvey P. Dale_, Mar 10 2023 *)
%K A007681 nonn
%O A007681 0,2
%A A007681 _N. J. A. Sloane_