(17-(-1)^n)/2.

Terms

a(0) =8a(1) =9a(2) =8a(3) =9a(4) =8a(5) =9a(6) =8a(7) =9a(8) =8a(9) =9a(10) =8a(11) =9a(12) =8a(13) =9a(14) =8a(15) =9a(16) =8a(17) =9a(18) =8a(19) =9a(20) =8a(21) =9a(22) =8a(23) =9a(24) =8a(25) =9a(26) =8a(27) =9a(28) =8a(29) =9