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 A376749 #21 Oct 12 2024 15:37:30
%S A376749 0,1,874,10741819,1870851589562,5465007068038102643,
%T A376749 269482732023591671431784330,221537990355601030571170905795094315,
%U A376749 3007205014171762201565124875608675533096268906,669557518440386985607930852942771727146772232484581602227,2433673642945425535196140161775877796522974318753784273286700783313050
%N A376749 Number of non-isomorphic colorings of a toroidal n X n grid using exactly four swappable colors.
%D A376749 F. Harary and E. Palmer, Graphical Enumeration, Academic Press, 1973.
%H A376749 Marko Riedel et al., <a href="https://math.stackexchange.com/questions/2506511/">Burnside lemma and translational symmetries of the torus.</a>
%H A376749 Marko Riedel, <a href="/A376749/a376749_1.maple.txt">Maple code for sequence.</a>
%F A376749 a(n) = (1/(n^2*4!))*(Sum_{sigma in S_4} Sum_{d|n} Sum_{f|n} phi(d) phi(f) [[forall j_l(sigma) > 0 : l|lcm(d,f) ]] P(gcd(d,f)*(n/d)*(n/f), sigma)) where P(F, sigma) = F! [z^F] Product_{l=1..4} (exp(lz)-1)^j_l(sigma). The notation j_l(sigma) is from the Harary text and gives the number of cycles of length l in the permutation sigma. [[.]] is an Iverson bracket.
%Y A376749 Main diagonal of A294793.
%Y A376749 Cf. A376747, A376748, A376808, A376824.
%K A376749 nonn
%O A376749 1,3
%A A376749 _Marko Riedel_, Oct 03 2024