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 A212803 #22 May 19 2020 16:19:19
%S A212803 1,4,108,12800,6050000,11218701312,81959473720768,2376692369090150400,
%T A212803 275204089028043534645504,127722545775271195902771200000,
%U A212803 238045190395699755964859156456705024,1783083199654005767436422099232872202240000,53684915729010675246823790713834564866472376291328
%N A212803 Number of Eulerian circuits in the Cartesian product of two directed cycles of lengths n.
%H A212803 Andrew Howroyd, <a href="/A212803/b212803.txt">Table of n, a(n) for n = 1..50</a>
%H A212803 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 A212803 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 A212803 Array[a, 12] // Round (* _Jean-François Alcover_, Sep 02 2019 *)
%Y A212803 Main diagonal of A212801.
%Y A212803 Cf. A054759, A297385.
%K A212803 nonn
%O A212803 1,2
%A A212803 _N. J. A. Sloane_, May 27 2012
%E A212803 Name clarified by _Andrew Howroyd_, Jan 12 2018
%E A212803 Terms a(13) and beyond from _Andrew Howroyd_, May 19 2020