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 A214624 #21 Oct 31 2024 01:17:21
%S A214624 1,1,16,504,28800,2620800,348364800,63707212800,15343379251200,
%T A214624 4707627724800000,1792664637603840000,829619584788234240000,
%U A214624 458592296933263933440000,298435681233688170332160000,225843218230899155927040000000,196652982274555440023470080000000
%N A214624 Braid numbers B((2)^n->(2)^n).
%C A214624 The number of different possible outcomes when starting with n piles of 2 distinct playing cards and repeatedly moving a top card from either of these n piles to one of n new piles, until all new piles have height 2.
%H A214624 J. de Ruiter, <a href="http://www.liacs.nl/assets/Masterscripties/2012-09JohandeRuiter.pdf">Counting Classes of Klondike Solitaire Configurations</a>, Master's Thesis (2012), 48-58.
%F A214624 a(n) = (2*n)!-n^2*(2*n-2)! for n>0.
%F A214624 a(n) = (2*n)!*(3*n-2)/(4*n-2).
%F A214624 a(n) = a(n-1)*2*n*(2*n-3)*(3*n-2)/(3*n-5) for n>0.
%F A214624 a(n) = Sum_{i=1..n} a(n-i)*C(n,i)*C(n-1,i-1)*i!*(i-1)!*(2^(2*i-1)-1) for n>0.
%F A214624 a(n) = Sum_{i=0..n-1} a(i)*n!*(n-1)!*(2^(2*n-2*i-1)-1)/(i!)^2 for n>0. [corrected by _Jason Yuen_, Oct 27 2024]
%F A214624 a(n) = Sum_{i=0..n-1} a(i)*((2*n)!!*(2*n-2)!!/((2*i)!!)^2-n!*(n-1)!/(i!)^2) for n>0. [corrected by _Jason Yuen_, Oct 27 2024]
%o A214624 (PARI) a(n) = (2*n)!*(3*n-2)/(4*n-2); \\ _Michel Marcus_, Aug 18 2013
%K A214624 nonn,easy
%O A214624 0,3
%A A214624 _Johan de Ruiter_, Jul 23 2012
%E A214624 More terms from _Michel Marcus_, Aug 18 2013