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A087252
Numbers that are divisible by 4, but cannot be the largest peak value in a 3x+1 trajectory, regardless of the initial value.
3
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
1,1
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.
CROSSREFS
Cf. A025586.
Sequence in context: A196475 A253534 A255136 * A141274 A224613 A134618
KEYWORD
nonn
AUTHOR
Labos Elemer, Sep 08 2003
EXTENSIONS
Definition and example reworded by Jon E. Schoenfield, Sep 01 2013
STATUS
approved