A048073 Number of nonempty subsets of {1,2,...,n} in which exactly 2/3 of the elements are <= (n+2)/3.

0, 0, 0, 2, 3, 4, 12, 15, 18, 51, 63, 76, 220, 270, 325, 945, 1155, 1390, 4102, 5005, 6027, 17955, 21875, 26348, 79116, 96288, 116010, 350568, 426303, 513729, 1560449, 1896279, 2285569, 6972339, 8468163, 10208110, 31253950