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 A184264 #23 Jan 20 2018 16:12:45 %S A184264 3,7,14,40,108,362,1182,4150,14602,52588,190746,699600,2581428, %T A184264 9588742,35792568,134223910,505294128,1908896442,7233642930, %U A184264 27487869472,104715443852,399822696082,1529755490574,5864063066500,22517998808028,86607689013412,333599974893066 %N A184264 Number of distinct n X 2 toroidal binary arrays. %H A184264 Alois P. Heinz, <a href="/A184264/b184264.txt">Table of n, a(n) for n = 1..1000</a> %H A184264 S. N. Ethier, <a href="http://arxiv.org/abs/1301.2352">Counting toroidal binary arrays</a>, arXiv preprint arXiv:1301.2352, 2013 and <a href="https://cs.uwaterloo.ca/journals/JIS/VOL16/Ethier/ethier2.html">J. Int. Seq. 16 (2013) #13.4.7</a> . %F A184264 a(n) ~ 2^(2*n-1) / n. - _Vaclav Kotesovec_, Sep 04 2014 %p A184264 with(numtheory): %p A184264 a:= n-> add(add(phi(c)*phi(d) *2^(2*n/ilcm(c, d)), %p A184264 d=divisors(n)), c=[1,2])/(2*n): %p A184264 seq(a(n), n=1..30); # _Alois P. Heinz_, Aug 25 2012 %Y A184264 Column 2 of A184271. %K A184264 nonn %O A184264 1,1 %A A184264 _R. H. Hardin_, Jan 10 2011 %E A184264 More terms from _Alois P. Heinz_, Aug 25 2012