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 A307923 #16 Feb 20 2025 08:39:09
%S A307923 0,1,16,744,56256,6385920,1018114560,217234805760,59809766768640,
%T A307923 20651520261980160,8740913386202726400,4451168534087349043200,
%U A307923 2685007039858238501683200,1893459488121880710532300800,1543515756205349079583241011200,1440363330182802737753009160192000
%N A307923 Number of (undirected) Hamiltonian cycles in the n-cocktail party graph.
%H A307923 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CocktailPartyGraph.html">Cocktail Party Graph</a>
%H A307923 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HamiltonianCycle.html">Hamiltonian Cycle</a>
%F A307923 a(n) = A129348(n)/2.
%t A307923 Join[{0}, Table[Gamma[2 n] Hypergeometric1F1[-n, 1 - 2 n, -2]/2, {n, 2, 20}]] (* _Eric W. Weisstein_, Feb 20 2025 *)
%t A307923 Join[{0}, RecurrenceTable[{-4 (1 + n) (2 + n) (5 + 2 n) a[n] - 2 (2 + n) (17 + 16 n + 4 n^2) a[n + 1] + (3 + 2 n) a[n + 2] == 0, a[1] == 1, a[2] == 16}, a[n], {n, 20}]] (* _Eric W. Weisstein_, Feb 20 2025 *)
%Y A307923 Cf. A129348, A167987, A307935.
%K A307923 nonn
%O A307923 1,3
%A A307923 _Eric W. Weisstein_, May 06 2019