47071589412domain: NAppears in sequencesa(n) = (3^n - 3)/2.at n=22A029858a(n) = 6 * A015518(n).at n=22A120471a(0) = 1, a(1) = 3, a(n) = 3*a(n-1) + 3 for n > 1.at n=22A123109a(n) = phi(3^n+1), where phi is Euler's totient function (A000010).at n=23A366579