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 A376748 #20 Oct 12 2024 15:37:35
%S A376748 0,3,345,447156,5647919665,694881637942816,813943290958393433377,
%T A376748 8941884948534360647405572800,912400181570021638669407666368774097,
%U A376748 858962534553352212055863239761275173880606456,7425662396340624836407113113710889289196975262054947345,587417576454184723055270940786413231085263155884260701824558793960
%N A376748 Number of non-isomorphic colorings of a toroidal n X n grid using exactly three swappable colors.
%D A376748 F. Harary and E. Palmer, Graphical Enumeration, Academic Press, 1973.
%H A376748 Marko Riedel et al., <a href="https://math.stackexchange.com/questions/2506511/">Burnside lemma and translational symmetries of the torus.</a>
%H A376748 Marko Riedel, <a href="/A376748/a376748_1.maple.txt">Maple code for sequence.</a>
%F A376748 a(n) = (1/(n^2*3!))*(Sum_{sigma in S_3} 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..3} (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 A376748 Main diagonal of A294792.
%Y A376748 Cf. A376747, A376749, A376808, A376823.
%K A376748 nonn
%O A376748 1,2
%A A376748 _Marko Riedel_, Oct 03 2024