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 A362900 #8 May 10 2023 22:38:53
%S A362900 1,0,1,9,162,4527,172335,7861940,416446379,25076668511,1692214417496,
%T A362900 126525497074469,10384653020019554,928348695659951013,
%U A362900 89797089935616345473,9344984104905250973209,1041167026926648579218267,123655975822561996200923033,15595901625395079379351443550
%N A362900 Number of nonisomorphic unordered pairs of fixed-point-free endofunctions on an n-set.
%C A362900 Isomorphism is up to permutation of the elements of the n-set.
%H A362900 Andrew Howroyd, <a href="/A362900/b362900.txt">Table of n, a(n) for n = 0..50</a>
%e A362900 In the following example the notation 211 corresponds to the fixed-point-free mapping {1->2, 2->1, 3->1}.
%e A362900 The a(3) = 9 nonisomorphic pairs of endofunctions are: {211, 211}, {211, 212}, {211, 231}, {211, 232}, {211, 311}, {211, 312}, {211, 332}, {231, 231}, {231, 312}.
%Y A362900 Column k=2 of A362899.
%Y A362900 Cf. A054745 (allowing fixed-points).
%K A362900 nonn
%O A362900 0,4
%A A362900 _Andrew Howroyd_, May 10 2023