a(n) = 2^n*(n + 2) + (n - 7)*n/2 - 2.

Terms

a(0) =1a(1) =9a(2) =32a(3) =88a(4) =217a(5) =507a(6) =1150a(7) =2562a(8) =5639a(9) =12301a(10) =26644a(11) =57372a(12) =122917a(13) =262191a(14) =557114a(15) =1179718a(16) =2490451a(17) =5242977a(18) =11010160a(19) =23068800a(20) =48234641a(21) =100663459a(22) =209715382a(23) =436207818a(24) =905969887a(25) =1879048437a(26) =3892314380a(27) =8053063972a(28) =16642998589a(29) =34359738711