A184269 - OEIS

%I #20 Jan 20 2018 16:14:49

%S 20,1182,99880,9587580,981706832,104715443852,11488774559744,

%T 1286742755471400,146402730743793240,16865594582168158776,

%U 1962541914958813595480,230271584688553159320640,27207473390887478569212080,3233802551602631768613571584

%N Number of distinct n X 7 toroidal binary arrays.

%H Vaclav Kotesovec, <a href="/A184269/b184269.txt">Table of n, a(n) for n = 1..470</a>

%H 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 a(n) ~ 128^n / (7*n). - _Vaclav Kotesovec_, Sep 04 2014

%p with(numtheory):

%p a:= n-> add(add(phi(c)*phi(d) *2^(7*n/ilcm(c, d)),

%p         d=divisors(n)), c=[1,7])/(7*n):

%p seq(a(n), n=1..20);  # _Alois P. Heinz_, Aug 25 2012

%Y Column 7 of A184271.

%K nonn

%O 1,1

%A _R. H. Hardin_, Jan 10 2011

%E More terms from _Alois P. Heinz_, Aug 25 2012