a(n) = 10*n^2 - 1.

Terms

a(0) =9a(1) =39a(2) =89a(3) =159a(4) =249a(5) =359a(6) =489a(7) =639a(8) =809a(9) =999a(10) =1209a(11) =1439a(12) =1689a(13) =1959a(14) =2249a(15) =2559a(16) =2889a(17) =3239a(18) =3609a(19) =3999a(20) =4409a(21) =4839a(22) =5289a(23) =5759a(24) =6249a(25) =6759a(26) =7289a(27) =7839a(28) =8409a(29) =8999