A087252 Numbers that are divisible by 4, but cannot be the largest peak value in a 3x+1 trajectory, regardless of the initial value.

12, 28, 36, 44, 60, 76, 92, 108, 120, 124, 140, 156, 164, 172, 188, 204, 216, 220, 236, 248, 252, 268, 284, 292, 300, 316, 328, 332, 348, 364, 376, 380, 388, 396, 412, 420, 428, 432, 436, 440, 444, 460, 476, 484, 492, 496, 500, 504, 508, 516, 524, 540, 548

Offset: 1

Author

Labos Elemer, Sep 08 2003

Keywords

• nonn

Comments

It is provable that (beyond 1 and 2) the largest peak value in any 3x+1 (Collatz) trajectory must be a multiple of 4. However, an infinite number of multiples of 4 exist that cannot be the largest peak value of such a trajectory. E.g., no integer of the form 16k+12 = 4*(4k+3) (where k is a nonnegative integer) can be a largest peak value, because the trajectory immediately after the value 16k+12 would consist of the values 8k+6, 4k+3, 12k+10, 6k+5, and 18k+16, which exceeds 16k+12.

Links

• Index entries for sequences related to 3x+1 (or Collatz) problem

Crossrefs

Cf. A025586.

Extensions

Definition and example reworded by Jon E. Schoenfield, Sep 01 2013