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 A184272 #17 Oct 31 2017 21:05:13
%S A184272 4,76,29184,268447936,45035996274688,131176846752109387776,
%T A184272 6467605103205252048452583424,5316911983139663492479919370381869056,
%U A184272 72172920362019897195243695442781187577923764224,16069380442589902755419620923449655543228876820136712994816
%N A184272 Number of distinct n X n toroidal 0..3 arrays.
%H A184272 Andrew Howroyd, <a href="/A184272/b184272.txt">Table of n, a(n) for n = 1..25</a>
%t A184272 T[n_, k_] := (1/(n*k))*Sum[Sum[EulerPhi[c]*EulerPhi[d]*4^(n*k/LCM[c, d]), {d, Divisors[k]}], {c, Divisors[n]}]; a[n_] := T[n, n]; Array[a, 10] (* _Jean-François Alcover_, Oct 31 2017, after _Andrew Howroyd_ *)
%Y A184272 Diagonal of A184277.
%K A184272 nonn
%O A184272 1,1
%A A184272 _R. H. Hardin_, Jan 10 2011
%E A184272 Terms a(6) and beyond from _Andrew Howroyd_, Sep 27 2017