In 101 Okey the ace (the 1) is low only, so a sequence like 12-13-1 is not valid.

The 1 can begin a run as 1-2-3, but it cannot wrap around above the 13. This differs from some other variants, so newcomers coming from classic Okey should note it. Because the 1 counts as a low tile, it also carries a low point value when you total your opening melds. Keeping this rule in mind prevents you from planning an illegal run that the game will reject.