A047161 Number of nonempty subsets of {1,2,...,n} in which exactly 1/3 of the elements are <= n/2.

0, 0, 1, 2, 6, 9, 21, 30, 70, 100, 235, 335, 791, 1127, 2681, 3822, 9150, 13050, 31401, 44802, 108262, 154517, 374715, 534963, 1301235, 1858155, 4531423, 6472167, 15818791, 22597759, 55339849, 79067374, 193962894, 277164294