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 A292934 #11 Sep 27 2017 09:19:17
%S A292934 0,0,2,6,48,400,4140,49644,681296,10515600,180349380,3402380740,
%T A292934 70023004920,1561206957336,37485640585484,964345394431020,
%U A292934 26462386594676640,771532717446066208,23817889096309943892,776127882633846005268
%N A292934 E.g.f.: x^2/(x+3-2*exp(x)).
%C A292934 Number of associative and quasitrivial binary operations on {1,...,n} that have both neutral and annihilator elements.
%H A292934 M. Couceiro, J. Devillet, and J.-L. Marichal, <a href="http://arxiv.org/abs/1709.09162">Quasitrivial semigroups: characterizations and enumerations</a>, arXiv:1709.09162 [math.RA], 2017.
%F A292934 a(n) = n*(n-1)*A292932(n-2).
%F A292934 a(n) ~ n! / ((r-1) * (r-3)^(n-1)), where r = -LambertW(-1, -2*exp(-3)) = 3.5830738760366909976807989989303134394318270218566... - _Vaclav Kotesovec_, Sep 27 2017
%Y A292934 Cf. A292932, A292933.
%K A292934 nonn,easy
%O A292934 0,3
%A A292934 _Jean-Luc Marichal_, Sep 27 2017