a(n) = 4*2^n - 3*n - 5.

Terms

a(0) =-1a(1) =0a(2) =5a(3) =18a(4) =47a(5) =108a(6) =233a(7) =486a(8) =995a(9) =2016a(10) =4061a(11) =8154a(12) =16343a(13) =32724a(14) =65489a(15) =131022a(16) =262091a(17) =524232a(18) =1048517a(19) =2097090a(20) =4194239a(21) =8388540a(22) =16777145a(23) =33554358a(24) =67108787a(25) =134217648a(26) =268435373a(27) =536870826a(28) =1073741735a(29) =2147483556