5230176600domain: NAppears in sequencesa(n) = (3^n - 3)/2.at n=20A029858a(n) = 6 * A015518(n).at n=20A120471a(0) = 1, a(1) = 3, a(n) = 3*a(n-1) + 3 for n > 1.at n=20A123109a(n) = 3*A132357(n).at n=19A135264