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 A333796 #16 Apr 07 2020 10:38:32 %S A333796 1,2,22,716,73346,23374544,23037365786,69630317879888 %N A333796 Number of self-avoiding closed paths on an n X n grid which pass through all points on the diagonal connecting NW and SE corners. %C A333796 a(11) = 18267559028025887599256. %e A333796 a(2) = 1; %e A333796 +--* %e A333796 | | %e A333796 *--+ %e A333796 a(3) = 2; %e A333796 +--*--* +--* %e A333796 | | | | %e A333796 *--+ * * +--* %e A333796 | | | | %e A333796 *--+ *--*--+ %e A333796 a(4) = 22; %e A333796 +--*--*--* +--*--*--* +--*--*--* %e A333796 | | | | | | %e A333796 *--+--* * *--+--* * *--+--* * %e A333796 | | | | | | %e A333796 *--*--+ * *--+ * + * %e A333796 | | | | | | %e A333796 *--*--*--+ *--*--+ *--+ %e A333796 +--*--*--* +--*--*--* +--*--*--* %e A333796 | | | | | | %e A333796 *--+ *--* *--+ *--* *--+ * %e A333796 | | | | | | %e A333796 *--* +--* * +--* *--+ * %e A333796 | | | | | | %e A333796 *--*--*--+ *--*--+ *--+ %e A333796 +--*--*--* +--*--*--* +--*--*--* %e A333796 | | | | | | %e A333796 * +--*--* * +--* * * +--* * %e A333796 | | | | | | | | | | %e A333796 * *--+--* *--* + * * * + * %e A333796 | | | | | | | | %e A333796 *--*--*--+ *--+ *--* *--+ %e A333796 +--*--* +--*--* +--*--* %e A333796 | | | | | | %e A333796 *--+ *--* *--+ * *--+ * %e A333796 | | | | | | %e A333796 *--+ * *--* +--* * +--* %e A333796 | | | | | | %e A333796 *--+ *--*--*--+ *--*--+ %e A333796 +--*--* +--* *--* +--* *--* %e A333796 | | | | | | | | | | %e A333796 * +--* * +--* * * +--* * %e A333796 | | | | | | %e A333796 * *--+--* *--*--+ * * *--+ * %e A333796 | | | | | | | | %e A333796 *--*--*--+ *--+ *--* *--+ %e A333796 +--* *--* +--* +--* %e A333796 | | | | | | | | %e A333796 * + * * * +--*--* * +--*--* %e A333796 | | | | | | | | %e A333796 * *--+ * *--*--+ * * *--+ * %e A333796 | | | | | | | | %e A333796 *--*--*--+ *--+ *--* *--+ %e A333796 +--* +--* +--* %e A333796 | | | | | | %e A333796 * +--* * +--* * + *--* %e A333796 | | | | | | | | %e A333796 *--* +--* * +--* * *--+ * %e A333796 | | | | | | %e A333796 *--*--+ *--*--*--+ *--*--*--+ %e A333796 +--* %e A333796 | | %e A333796 * + %e A333796 | | %e A333796 * *--+--* %e A333796 | | %e A333796 *--*--*--+ %o A333796 (Python) %o A333796 # Using graphillion %o A333796 from graphillion import GraphSet %o A333796 import graphillion.tutorial as tl %o A333796 def A333796(n): %o A333796 universe = tl.grid(n - 1, n - 1) %o A333796 GraphSet.set_universe(universe) %o A333796 cycles = GraphSet.cycles() %o A333796 points = [i + 1 for i in range(n * n) if i % n - i // n == 0] %o A333796 for i in points: %o A333796 cycles = cycles.including(i) %o A333796 return cycles.len() %o A333796 print([A333796(n) for n in range(2, 10)]) %Y A333796 Cf. A333455, A333464, A333466, A333795. %K A333796 nonn,more %O A333796 2,2 %A A333796 _Seiichi Manyama_, Apr 05 2020