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 A308362 #21 Aug 19 2019 16:50:50
%S A308362 1,5,23,162,1382,14236,170872,2344530,36188534,620652000,11708927276,
%T A308362 240976560622,5372724404530,129002764437228,3318690040767224,
%U A308362 91067432174168202,2655146132506208558,81966680980803524728,2670959894858615348356,91616517379045122841830
%N A308362 Number of (2k+1)-ary quasitrivial semigroups on an n-element set.
%C A308362 Number of (2k+1)-ary associative and quasitrivial operations on an n-element set.
%H A308362 Michael De Vlieger, <a href="/A308362/b308362.txt">Table of n, a(n) for n = 1..413</a>
%H A308362 M. Couceiro, J. Devillet, <a href="https://arxiv.org/abs/1904.05968">All quasitrivial n-ary semigroups are reducible to semigroups</a>, arXiv:1904.05968 [math.RA], 2019.
%H A308362 Jimmy Devillet, Miguel Couceiro, <a href="http://orbilu.uni.lu/handle/10993/39720">Characterizations and enumerations of classes of quasitrivial n-ary semigroups</a>, 98th Workshop on General Algebra (AAA98, Dresden, Germany 2019).
%F A308362 a(n) = A308352(n) + A292933(n) + A308354(n) for n >= 1.
%F A308362 a(n) = A292932(n) + binomial(n,2)*A292932(n-2) for n >= 2.
%F A308362 E.g.f.: (2 + x^2)/(6 - 4*exp(x) + 2*x). - _Vaclav Kotesovec_, Jun 05 2019
%F A308362 a(n) ~ n! * (r^2 - 6*r + 11) / (2*(r-1) * (r-3)^(n+1)), where r = -LambertW(-1, -2*exp(-3)). - _Vaclav Kotesovec_, Jun 05 2019
%t A308362 nmax = 20; Rest[CoefficientList[Series[(2 + x^2)/(6 - 4*E^x + 2*x), {x, 0, nmax}], x] * Range[0, nmax]!] (* _Vaclav Kotesovec_, Jun 05 2019 *)
%Y A308362 Cf. A308352, A308354, A292932, A292933.
%K A308362 nonn,easy
%O A308362 1,2
%A A308362 _J. Devillet_, May 22 2019