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%I #22 May 19 2020 16:19:19
%S 1,4,108,12800,6050000,11218701312,81959473720768,2376692369090150400,
%T 275204089028043534645504,127722545775271195902771200000,
%U 238045190395699755964859156456705024,1783083199654005767436422099232872202240000,53684915729010675246823790713834564866472376291328
%N Number of Eulerian circuits in the Cartesian product of two directed cycles of lengths n.
%H Andrew Howroyd, <a href="/A212803/b212803.txt">Table of n, a(n) for n = 1..50</a>
%H Germain Kreweras, <a href="https://doi.org/10.1016/0095-8956(78)90021-7">Complexité et circuits Eulériens dans les sommes tensorielles de graphes</a>, J. Combin. Theory, B 24 (1978), 202-212.
%t a[n_] := Product[2-E^(2 h Pi I/n)-E^(2 k Pi I/n), {h, 1, n-1}, {k, 1, n-1}];
%t Array[a, 12] // Round (* _Jean-François Alcover_, Sep 02 2019 *)
%Y Main diagonal of A212801.
%Y Cf. A054759, A297385.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, May 27 2012
%E Name clarified by _Andrew Howroyd_, Jan 12 2018
%E Terms a(13) and beyond from _Andrew Howroyd_, May 19 2020
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