22906492247domain: NAppears in sequencesa(n) = (2^n + 3 - 7*(-1)^n + 3*0^n)/6; or a(0) = 0 and for n > 0, a(n) = A005578(n-1) - (-1)^n.at n=37A135351a(n) = (4^n + 5)/3.at n=18A163834