21516800domain: NAppears in sequencesNumber of n X n matrices over GF(3) with rank 1.at n=7A060868Cogrowth sequence of the 18-element group S3 X C3 = <S,T,U | S^3, T^2, U^3, (ST)^2, [S,U], [T,U]>.at n=18A378109Array read by ascending antidiagonals: A(n, k) = (k^n - 1)^2/(k - 1), with k >= 2.at n=46A379587