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 A102687 #19 Jan 07 2024 14:18:53
%S A102687 1,1,3,12,100,1075,13356,197764,3403576,66159405,1438338070
%N A102687 Number of different squares of labeled mappings of a finite set of n elements into itself.
%C A102687 Let A be a finite set of cardinal n, F be the set of mappings from A to A and F_2 be the subset of F including all g such that there exists f in F with g = fof (composition of f with itself). Then a(n) = #F_2.
%t A102687 f[a_][b_] /; Length[a]==Length[b] := Table[b[[a[[i]]]], {i, 1, Length[a]}];
%t A102687 A[n_, k_] := Nest[f[#], Range[n], k]& /@ Tuples[Range[n], {n}] // Union // Length;
%t A102687 a[n_] := a[n] = A[n, 2];
%t A102687 Table[Print[n, " ", a[n]]; a[n], {n, 0, 7}] (* _Jean-François Alcover_, May 27 2019 *)
%Y A102687 Cf. A102709.
%Y A102687 Column k=2 of A247026.
%K A102687 nonn,more
%O A102687 0,3
%A A102687 Eric Wegrzynowski (Eric.Wegrzynowski(AT)lifl.fr), Feb 03 2005
%E A102687 a(7) from _Vladeta Jovovic_, Feb 05 2005
%E A102687 a(8) and a(9) from _Joshua Zucker_, May 18 2006
%E A102687 a(0) from _Alois P. Heinz_, Sep 09 2014
%E A102687 a(10) from _Bert Dobbelaere_, Jan 24 2019