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 A066211 #15 Jun 15 2018 20:51:56
%S A066211 1,3,17,157,2081,36101,773665,19726085,582913217,19582414021,
%T A066211 736891600001,30699450566885,1402556105125345,69719685409234277,
%U A066211 3745929254826233441,216310377722912693701,13359435408855851031425,878701820865582786218885
%N A066211 a(n) = Sum_{j=0..n} (2*n)!/(2*n-j)!.
%H A066211 Harry J. Smith, <a href="/A066211/b066211.txt">Table of n, a(n) for n = 0..100</a>
%F A066211 Recurrence: (8*n^3 - 34*n^2 + 47*n - 20)*a(n) = (32*n^5 - 120*n^4 + 144*n^3 - 56*n^2 + 7*n + 2)*a(n-1) - 2*(2*n-3)*(32*n^5 - 144*n^4 + 238*n^3 - 161*n^2 + 38*n - 1)*a(n-2) + 4*(n-2)*(2*n-5)*(2*n-3)*(8*n^3 - 10*n^2 + 3*n + 1)*a(n-3). - _Vaclav Kotesovec_, Dec 29 2013
%F A066211 a(n) ~ 2^(2*n+1/2) * n^n / exp(n). - _Vaclav Kotesovec_, Dec 29 2013
%t A066211 Table[Sum[(2*n)!/(2*n-j)!, {j, 0, n}], {n, 0, 20}] (* _Vaclav Kotesovec_, Dec 29 2013 *)
%o A066211 (PARI) { for (n=0, 100, s=0; for (j=0, n, s+=(2*n)!/(2*n - j)!); write("b066211.txt", n, " ", s) ) } \\ _Harry J. Smith_, Feb 06 2010
%K A066211 nonn
%O A066211 0,2
%A A066211 _N. J. A. Sloane_, Dec 17 2001