"Station-keeping Collatz numbers": a(n) is the smallest even number whose Collatz ('3x+1') trajectory, after its initial step downward, is directed back toward its starting value at each of its next n steps.

A304363

"Station-keeping Collatz numbers": a(n) is the smallest even number whose Collatz ('3x+1') trajectory, after its initial step downward, is directed back toward its starting value at each of its next n steps.