Write n in base of Catalan numbers, then interpret as if written in base 3.

Terms

a(0) =0a(1) =1a(2) =3a(3) =4a(4) =6a(5) =9a(6) =10a(7) =12a(8) =13a(9) =15a(10) =18a(11) =19a(12) =21a(13) =22a(14) =27a(15) =28a(16) =30a(17) =31a(18) =33a(19) =36a(20) =37a(21) =39a(22) =40a(23) =42a(24) =45a(25) =46a(26) =48a(27) =49a(28) =54a(29) =55