What does 13 c on a t b including u mean?

The phrase "13 c on a t b including u" is a riddle that stands for "13 clues on a treasure boat including you." It typically refers to a fun way of presenting a puzzle or challenge, where each letter or number represents a Word or concept. In this case, "c" stands for clues, "t" for treasure, "b" for boat, and "u" represents the person involved in the adventure.