Number of tripling steps to reach 1 from n in '3x+1' problem, or -1 if 1 is never reached.

Terms

a(0) =0a(1) =0a(2) =2a(3) =0a(4) =1a(5) =2a(6) =5a(7) =0a(8) =6a(9) =1a(10) =4a(11) =2a(12) =2a(13) =5a(14) =5a(15) =0a(16) =3a(17) =6a(18) =6a(19) =1a(20) =1a(21) =4a(22) =4a(23) =2a(24) =7a(25) =2a(26) =41a(27) =5a(28) =5a(29) =5