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 A140521 #18 Feb 16 2025 08:33:08 %S A140521 1,6,32,5660,4924128,45707720232,3244086234829248, %T A140521 1923484178952564643368 %N A140521 Number of directed "king tours" on an n X n board. %C A140521 Or, number of directed Hamiltonian cycles in the graph P_n X P_n. %C A140521 If the direction of the tour is not taken into account, the numbers for n > 1 must be halved (see A140519). %C A140521 Computed using ZDDs (ZDD = "reduced, order, zero-suppressed binary decision diagram"). %D A140521 Donald E. Knuth, The Art of Computer Programming, Vol. 4, fascicle 1, section 7.1.4, p. 117, Addison-Wesley, 2009. %H A140521 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HamiltonianCycle.html">Hamiltonian Cycle</a> %H A140521 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/KingGraph.html">King Graph</a> %H A140521 <a href="/index/Gra#graphs">Index entries for sequences related to graphs, Hamiltonian</a> %Y A140521 Cf. A001230, A140519. %K A140521 nonn,walk %O A140521 1,2 %A A140521 _Don Knuth_, Jul 26 2008