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 A201996 #19 Jul 18 2025 10:13:11
%S A201996 1,1,4,27,252,3000,43380,737730,14419440,318381840,7835486400,
%T A201996 212634298800,6307073942400,202983948367200,7044249755743200,
%U A201996 262198957638618000,10419369722457696000,440257835691561888000,19709455059507717504000,931885122471464345184000,46401644730376725229440000
%N A201996 The number of endofunctions on n points such that all recurrent elements have at most 3 preimages and all nonrecurrent elements have at most 2 preimages.
%H A201996 Michael De Vlieger, <a href="/A201996/b201996.txt">Table of n, a(n) for n = 0..390</a>
%H A201996 Giulio Cerbai and Anders Claesson, <a href="https://arxiv.org/abs/2507.09304">Counting fixed-point-free Cayley permutations</a>, arXiv:2507.09304 [math.CO], 2025. See p. 25.
%F A201996 E.g.f.: 1/(1-A(x)) where A(x) is the e.g.f. for A036774.
%F A201996 a(n) ~ n! * (5/2)^n/5. - _Vaclav Kotesovec_, Sep 24 2013
%t A201996 a = (1 - x - (1 - 2 x - x^2)^(1/2))/x; Range[0, 20]! CoefficientList[Series[1/(1 - a), {x, 0, 20}], x]
%K A201996 nonn
%O A201996 0,3
%A A201996 _Geoffrey Critzer_, Dec 07 2011