A187264 Number of nonempty subsets of {1, 2, ..., n} with <=3 pairwise coprime elements.

1, 3, 7, 11, 21, 25, 43, 54, 73, 83, 125, 136, 194, 215, 245, 278, 374, 396, 516, 552, 614, 662, 834, 871, 1018, 1087, 1215, 1285, 1555, 1592, 1900, 2023, 2181, 2298, 2506, 2581, 3013, 3160, 3378, 3497, 4027, 4105, 4689, 4875, 5103

Offset: 1

Author

Alois P. Heinz, Mar 07 2011

Keywords

• nonn

Examples

			a(4) = 11 because there are 11 nonempty subsets of {1,2,3,4} with <=3 pairwise coprime elements: {1}, {2}, {3}, {4}, {1,2}, {1,3}, {1,4}, {2,3}, {3,4}, {1,2,3}, {1,3,4}.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..10000

Crossrefs

Column 3 of triangle A187262. First differences are A186987.

Formula

a(n) = A187262(n,3).