a(n) = (-1)^n + (-2)^n - (-3)^n.

Terms

a(0) =1a(1) =0a(2) =-4a(3) =18a(4) =-64a(5) =210a(6) =-664a(7) =2058a(8) =-6304a(9) =19170a(10) =-58024a(11) =175098a(12) =-527344a(13) =1586130a(14) =-4766584a(15) =14316138a(16) =-42981184a(17) =129009090a(18) =-387158344a(19) =1161737178a(20) =-3485735824a(21) =10458256050a(22) =-31376865304a(23) =94134790218a(24) =-282412759264a(25) =847255055010