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

Terms

a(0) =1a(1) =0a(2) =-2a(3) =-4a(4) =-4a(5) =2a(6) =22a(7) =72a(8) =184a(9) =422a(10) =914a(11) =1916a(12) =3940a(13) =8010a(14) =16174a(15) =32528a(16) =65264a(17) =130766a(18) =261802a(19) =523908a(20) =1048156a(21) =2096690a(22) =4193798a(23) =8388056a(24) =16776616a(25) =33553782a(26) =67108162a(27) =134216972a(28) =268434644a(29) =536870042