a(n) = (7 + (-1)^n + 6*n)*2^(n-3).

Terms

a(0) =1a(1) =3a(2) =10a(3) =24a(4) =64a(5) =144a(6) =352a(7) =768a(8) =1792a(9) =3840a(10) =8704a(11) =18432a(12) =40960a(13) =86016a(14) =188416a(15) =393216a(16) =851968a(17) =1769472a(18) =3801088a(19) =7864320a(20) =16777216a(21) =34603008a(22) =73400320a(23) =150994944a(24) =318767104a(25) =654311424a(26) =1375731712a(27) =2818572288a(28) =5905580032