Numbers n such that the trajectory of n under the `3x+1' map reaches n - 1.

Terms

a(0) =2a(1) =3a(2) =5a(3) =6a(4) =9a(5) =11a(6) =14a(7) =17a(8) =18a(9) =39a(10) =41a(11) =47a(12) =54a(13) =57a(14) =59a(15) =62a(16) =71a(17) =81a(18) =89a(19) =107a(20) =108a(21) =161a(22) =252a(23) =284a(24) =378a(25) =639a(26) =651a(27) =959a(28) =977a(29) =1368