OFFSET
1,3
EXAMPLE
For n = 4 we have a(n) = 7, since the divisors <=4 of 1,2,..., 12 are
{1}, {1,2}, {1,3}, {1,2,4}, {1}, {1,2,3}, {1}, {1,2,4}, {1,3}, {1,2}, {1}, and {1,2,3,4}, and only 7 of these have odd cardinality.
CROSSREFS
KEYWORD
nonn
AUTHOR
Jeffrey Shallit, Apr 16 2014
STATUS
approved