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 A006326 M3931 #28 Jun 01 2019 11:30:35
%S A006326 1,5,24,122,680,4155,27776,202084,1592064,13513825,123025408,
%T A006326 1196165886,12374422528,135740585015,1573990072320,19239037403528,
%U A006326 247255523459072,3333340694137725,47039231504678912,693488743931379010,10661950808321949696,170659875799127955955
%N A006326 Total preorders.
%D A006326 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A006326 G. Kreweras, <a href="http://www.numdam.org/item?id=MSH_1976__53__5_0">Les préordres totaux compatibles avec un ordre partiel</a>, Math. Sci. Humaines No. 53 (1976), 5-30.
%H A006326 G. Kreweras, <a href="/A019538/a019538.pdf">Les préordres totaux compatibles avec un ordre partiel</a>, Math. Sci. Humaines No. 53 (1976), 5-30. (Annotated scanned copy)
%p A006326 # After _Alois P. Heinz_ in A000111:
%p A006326 b := proc(u, o) option remember;
%p A006326 `if`(u + o = 0, 1, add(b(o - 1 + j, u - j), j = 1..u)) end:
%p A006326 a := n -> (n-2)*b(n-1, 1)/2: seq(a(n), n = 3..23); # _Peter Luschny_, Oct 27 2017
%t A006326 b[u_, o_] := b[u, o] = If[u+o == 0, 1, Sum[b[o-1+j, u-j], {j, 1, u}]];
%t A006326 a[n_] := (n-2) b[n-1, 1]/2;
%t A006326 Array[a, 22, 3] (* _Jean-François Alcover_, Jun 01 2019, from Maple *)
%Y A006326 Cf. A000111, A079502.
%K A006326 nonn
%O A006326 3,2
%A A006326 _N. J. A. Sloane_
%E A006326 More terms from _Sean A. Irvine_, Mar 12 2017