a(n) = 2^n*(n^2 - n + 8)/8.

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =40a(5) =112a(6) =304a(7) =800a(8) =2048a(9) =5120a(10) =12544a(11) =30208a(12) =71680a(13) =167936a(14) =389120a(15) =892928a(16) =2031616a(17) =4587520a(18) =10289152a(19) =22937600a(20) =50855936a(21) =112197632a(22) =246415360a(23) =538968064a(24) =1174405120a(25) =2550136832a(26) =5519704064a(27) =11911823360a(28) =25635586048a(29) =55029268480