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

Terms

a(0) =1a(1) =-1a(2) =-4a(3) =-7a(4) =-8a(5) =-3a(6) =16a(7) =65a(8) =176a(9) =413a(10) =904a(11) =1905a(12) =3928a(13) =7997a(14) =16160a(15) =32513a(16) =65248a(17) =130749a(18) =261784a(19) =523889a(20) =1048136a(21) =2096669a(22) =4193776a(23) =8388033a(24) =16776592a(25) =33553757a(26) =67108136a(27) =134216945a(28) =268434616a(29) =536870013