Number of halving steps to reach 1 in '3x+1' problem, or -1 if this never happens.

Terms

a(0) =0a(1) =1a(2) =5a(3) =2a(4) =4a(5) =6a(6) =11a(7) =3a(8) =13a(9) =5a(10) =10a(11) =7a(12) =7a(13) =12a(14) =12a(15) =4a(16) =9a(17) =14a(18) =14a(19) =6a(20) =6a(21) =11a(22) =11a(23) =8a(24) =16a(25) =8a(26) =70a(27) =13a(28) =13a(29) =13