20176803domain: NAppears in sequencesNumber of free subsets of multiplicative group of GF(7^n).at n=8A007233a(n) = (7^n - 1)/2.at n=9A120741A sevens sequence: a(n) = (7^n - 1)/(2^(4 - 3*(n mod 2))).at n=9A152418Number of compositions of odd natural numbers into 9 parts <= n.at n=6A191680