Replace any decimal digit '1' with '2' and vice versa.

Terms

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