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 A124355 #14 Feb 16 2025 08:33:03
%S A124355 0,0,2,6,24,120,720,5040,40320,362880,3628800,39916800,479001600,
%T A124355 6227020800,87178291200,1307674368000,20922789888000,355687428096000,
%U A124355 6402373705728000,121645100408832000,2432902008176640000
%N A124355 Number of (directed) Hamiltonian cycles on the complete graph K_n.
%C A124355 a(n) is also the number of (directed) Hamiltonian paths on the complete graph K_{n-1}.
%H A124355 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CompleteGraph.html">Complete Graph</a>, <a href="https://mathworld.wolfram.com/HamiltonianCycle.html">Hamiltonian Cycle</a>, <a href="https://mathworld.wolfram.com/HamiltonianPath.html">Hamiltonian Path</a>.
%F A124355 a(1) = 0, a(2) = 0, a(n) = (n-1)! = A104150(n) for n > 2. - _Georg Fischer_, Oct 21 2018
%Y A124355 Cf. A000142, A104150.
%K A124355 nonn
%O A124355 1,3
%A A124355 _Eric W. Weisstein_, Nov 05 2006