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

Terms

a(0) =1a(1) =8a(2) =29a(3) =82a(4) =207a(5) =492a(6) =1129a(7) =2534a(8) =5603a(9) =12256a(10) =26589a(11) =57306a(12) =122839a(13) =262100a(14) =557009a(15) =1179598a(16) =2490315a(17) =5242824a(18) =11009989a(19) =23068610a(20) =48234431a(21) =100663228a(22) =209715129a(23) =436207542a(24) =905969587a(25) =1879048112a(26) =3892314029a(27) =8053063594a(28) =16642998183a(29) =34359738276