First, find the treasure chest.

There is something like a memo attached to the problem, but one side is not visible. Then, when you find the treasure chest, you can find the other note as well.

When comparing it with the other side, it seems that the triangular number in the middle is a clue. It seems that it is. It seems like the intention is to "advance one character."

In this way, if you proceed with "vghsd", "lxrsdqx", and "kdfdmc" one by one, ,,,?