795704domain: NAppears in sequencesNumber of nonempty subsets of {1,2,...,n} in which exactly 1/6 of the elements are <= (n-1)/2.at n=29A047180Number of nonempty subsets of {1,2,...,n} in which exactly 1/6 of the elements are <= (n-2)/2.at n=29A047191a(n) = (3^(n-1) - 1) * (3^n - 1)/2.at n=6A109774