a(n) = 9-n.

Terms

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