A375267 Number of iterations of the A375265 map to reach 1 starting from n, or -1 if 1 is never reached.

0, 1, 1, 2, 5, 2, 16, 3, 2, 6, 14, 3, 9, 17, 6, 4, 12, 3, 20, 7, 17, 15, 15, 4, 23, 10, 3, 18, 18, 7, 106, 5, 15, 13, 13, 4, 21, 21, 10, 8, 109, 18, 29, 16, 7, 16, 104, 5, 24, 24, 13, 11, 11, 4, 112, 19, 21, 19, 32, 8, 19, 107, 18, 6, 27, 16, 27, 14, 16, 14, 102

Offset: 1

Author

Paolo Xausa, Aug 09 2024

Keywords

• nonn
• easy

Examples

			a(10) = 6 because the trajectory 10 -> 5 -> 16 -> 8 -> 4 -> 2 -> 1 consists of 6 steps.
		

Links

• Paolo Xausa, Table of n, a(n) for n = 1..10000
• Index entries for sequences related to 3x+1 (or Collatz) problem.

Crossrefs

(Row lengths of A375266) - 1.

Cf. A006577, A006666, A375280.

Programs

Mathematica

A375265[n_] := Which[Divisible[n, 3], n/3, Divisible[n, 2], n/2, True, 3*n + 1];
Array[Length[NestWhileList[A375265, #, # > 1 &]] - 1 &, 100]