a(n) = n-21.

Terms

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