A241147 a(n) = the number of integers i in {1,2,...,L}, where L = lcm(1,2,...,n), having the property that the number of positive integer divisors of i that are less than or equal to n, is odd.

1, 1, 3, 7, 33, 33, 225, 405, 1305, 1235, 13635, 13635, 177705, 170775, 170181, 359073, 6106815, 5919705, 112887225, 109706355, 110362725, 107787735

Offset

1,3

Links

Table of n, a(n) for n=1..22.

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

Sequence in context: A074699 A115088 A089622 * A143967 A007646 A238314

Adjacent sequences: A241144 A241145 A241146 * A241148 A241149 A241150

Keyword

nonn

Author

Jeffrey Shallit, Apr 16 2014

Status

approved