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A326172
Number of nonempty subsets of {2..n} whose product is divisible by their sum.
2
0, 0, 1, 2, 3, 6, 12, 21, 34, 69, 140, 278, 561, 1144, 2367, 4936, 9503, 19368, 38202, 77911, 156458, 318911, 651462, 1329624, 2596458, 5144833, 10494839, 20500025, 40923643, 83620258, 164982516, 335873558, 651383048, 1310551707, 2655240565, 5295397093, 10338145110, 21052407259, 42748787713, 86078893923, 169349494068
OFFSET
0,4
EXAMPLE
The a(2) = 1 through a(7) = 21 subsets:
{2} {2} {2} {2} {2} {2}
{3} {3} {3} {3} {3}
{4} {4} {4} {4}
{5} {5} {5}
{2,3,5} {6} {6}
{3,4,5} {3,6} {7}
{2,3,5} {3,6}
{2,4,6} {2,3,5}
{3,4,5} {2,4,6}
{4,5,6} {2,5,7}
{3,4,5,6} {3,4,5}
{2,3,4,5,6} {3,4,7}
{3,5,7}
{4,5,6}
{2,3,6,7}
{2,5,6,7}
{3,4,5,6}
{3,5,6,7}
{2,3,4,5,6}
{2,3,4,5,7}
{2,4,5,6,7}
MATHEMATICA
Table[Length[Select[Subsets[Range[2, n], {1, n}], Divisible[Times@@#, Plus@@#]&]], {n, 0, 10}]
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jun 11 2019
EXTENSIONS
a(21)-a(29) from Alois P. Heinz, Jun 13 2019
a(30)-a(40) from Bert Dobbelaere, Jun 22 2019
STATUS
approved