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 A000779 #29 Sep 08 2022 08:44:28
%S A000779 1,4,22,162,1506,16950,224190,3408930,58596930,1123663590,23782729950,
%T A000779 550718680050,13849716607650,375904338960150,10952237584237950,
%U A000779 340947694234397250,11294123783425733250,396665528378000631750
%N A000779 a(n) = 2*(2n-1)!!-(n-1)!*2^(n-1), where (2n-1)!! is A001147(n).
%H A000779 Nathaniel Johnston, <a href="/A000779/b000779.txt">Table of n, a(n) for n = 1..250</a>
%H A000779 J. R. Stembridge, <a href="http://dx.doi.org/10.1090/S0002-9947-97-01805-9">Some combinatorial aspects of reduced words in finite Coxeter groups</a>, Trans. Amer. Math. Soc. 349 (1997), no. 4, 1285-1332.
%p A000779 seq(2*doublefactorial(2*n-1)-(n-1)!*2^(n-1), n=1..18); # _Nathaniel Johnston_, Jun 23 2011
%t A000779 Table[2*(2n-1)!! - (n-1)!*2^(n-1), {n, 1, 20}] (* _Jean-François Alcover_, Feb 11 2016 *)
%o A000779 (Magma) A001147:=func< n | n eq 0 select 1 else &*[ k: k in [1..2*n-1 by 2] ] >; [ 2*A001147(n)-Factorial(n-1)*2^(n-1): n in [1..20] ]; // _Klaus Brockhaus_, Jun 22 2011
%Y A000779 Cf. A001147.
%K A000779 nonn,easy
%O A000779 1,2
%A A000779 _N. J. A. Sloane_
%E A000779 More terms from _Sean A. Irvine_, Jun 13 2011