a(n) = n-39.

Terms

a(0) =-39a(1) =-38a(2) =-37a(3) =-36a(4) =-35a(5) =-34a(6) =-33a(7) =-32a(8) =-31a(9) =-30a(10) =-29a(11) =-28a(12) =-27a(13) =-26a(14) =-25a(15) =-24a(16) =-23a(17) =-22a(18) =-21a(19) =-20a(20) =-19a(21) =-18a(22) =-17a(23) =-16a(24) =-15a(25) =-14a(26) =-13a(27) =-12a(28) =-11a(29) =-10