a(n) = (1-2n)*2^n.

Terms

a(0) =1a(1) =-2a(2) =-12a(3) =-40a(4) =-112a(5) =-288a(6) =-704a(7) =-1664a(8) =-3840a(9) =-8704a(10) =-19456a(11) =-43008a(12) =-94208a(13) =-204800a(14) =-442368a(15) =-950272a(16) =-2031616a(17) =-4325376a(18) =-9175040a(19) =-19398656a(20) =-40894464a(21) =-85983232a(22) =-180355072a(23) =-377487360a(24) =-788529152a(25) =-1644167168a(26) =-3422552064a(27) =-7113539584a(28) =-14763950080