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 A368140 #16 Jul 09 2024 08:51:39 %S A368140 1,4,22,1154,337192,477360876,2872203226920,72057597041056852, %T A368140 7462505060326909791920,3169126500571693774150807456, %U A368140 5492677668532711895587506949961184,38716571525226776294594927800946276718944,1106936151351216411420589971585441310578379941760 %N A368140 Number of ways of tiling the n X n torus up to diagonal and antidiagonal reflection of the square by a tile that is fixed under only diagonal reflection. %H A368140 Peter Kagey, <a href="/A368140/a368140.pdf">Illustration of a(3)=22</a> %H A368140 Peter Kagey and William Keehn, <a href="https://arxiv.org/abs/2311.13072">Counting tilings of the n X m grid, cylinder, and torus</a>, arXiv: 2311.13072 [math.CO], 2023. See also <a href="https://cs.uwaterloo.ca/journals/JIS/VOL27/Kagey/kagey6.html">J. Int. Seq.</a>, (2024) Vol. 27, Art. No. 24.6.1, pp. A-21, A-24. %t A368140 A368140[n_] := 1/(4n^2)*(DivisorSum[n, Function[d, DivisorSum[n, Function[c, EulerPhi[c] EulerPhi[d] 2^(n^2/LCM[c, d])]]]] + n^2*If[EvenQ[n], (3*2^(n^2/2 - 2)), 0] + n*DivisorSum[n, Function[d, EulerPhi[d] If[EvenQ[d], 2^(n^2/(2 d) + 1), 2^((n^2 + n)/(2d))]]]) %Y A368140 Cf. A295223, A367526, A368139, A368141, A368142. %K A368140 nonn %O A368140 1,2 %A A368140 _Peter Kagey_, Dec 16 2023