20 in base 20-n.

Terms

a(0) =10a(1) =11a(2) =12a(3) =13a(4) =14a(5) =15a(6) =16a(7) =17a(8) =18a(9) =19a(10) =20a(11) =22a(12) =24a(13) =26a(14) =32a(15) =40a(16) =110a(17) =202a(18) =10100