%I #9 Feb 16 2025 08:33:55
%S 0,0,1,16,3216,9748992,554701578240,690468767270830080
%N Number of (undirected) Hamiltonian circuits in the n-triangular graph.
%H Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HamiltonianCycle.html">Hamiltonian Cycle</a>
%H Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TriangularGraph.html">Triangular Graph</a>
%F a(n) = A129349(n)/2.
%Y Cf. A129349.
%K nonn,more,hard,changed
%O 2,4
%A _Eric W. Weisstein_, May 06 2019