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

Terms

a(0) =-3a(1) =-5a(2) =-7a(3) =-5a(4) =17a(5) =115a(6) =473a(7) =1675a(8) =5537a(9) =17635a(10) =54953a(11) =168955a(12) =515057a(13) =1561555a(14) =4717433a(15) =14217835a(16) =42784577a(17) =128615875a(18) =386371913a(19) =1160164315a(20) =3482590097a(21) =10451964595a(22) =31364282393a(23) =94109624395a(24) =282362427617a(25) =847154391715