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Step Numbers 2.0
A ‘step number’ is a number consisting of at least 3 strictly increasing numbers with a fixed 'step size'. For example, 357 is a step number with 3 steps and step size 2, and 591317 is a step number with 4 steps and step size 4 (5|9|13|17).
We define a step number as "double-stepped" if the same number has both m steps with step size s, and n steps with step size t, with {m, s} ≠ {n, t}.
Challenger
Give the smallest double-stepped number.
Mastermind
Do double-stepped numbers exist with m = n, but s < t? If it exists, give the smallest number. If you think not, answer 0.