OFFSET
1,1
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..1000
S. N. Ethier, Counting toroidal binary arrays, arXiv preprint arXiv:1301.2352, 2013 and J. Int. Seq. 16 (2013) #13.4.7 .
FORMULA
a(n) ~ 2^(2*n-1) / n. - Vaclav Kotesovec, Sep 04 2014
MAPLE
with(numtheory):
a:= n-> add(add(phi(c)*phi(d) *2^(2*n/ilcm(c, d)),
d=divisors(n)), c=[1, 2])/(2*n):
seq(a(n), n=1..30); # Alois P. Heinz, Aug 25 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 10 2011
EXTENSIONS
More terms from Alois P. Heinz, Aug 25 2012
STATUS
approved