a(n) = 2^n*floor((5-2*n)/3).

Terms

a(0) =1a(1) =2a(2) =0a(3) =-8a(4) =-16a(5) =-64a(6) =-192a(7) =-384a(8) =-1024a(9) =-2560a(10) =-5120a(11) =-12288a(12) =-28672a(13) =-57344a(14) =-131072a(15) =-294912a(16) =-589824a(17) =-1310720a(18) =-2883584a(19) =-5767168a(20) =-12582912a(21) =-27262976a(22) =-54525952a(23) =-117440512a(24) =-251658240a(25) =-503316480a(26) =-1073741824a(27) =-2281701376a(28) =-4563402752a(29) =-9663676416