The horizontal number is odd, so is the vertical number. Let me take 3 as an example to illustrate:

There are three squares in the horizontal direction and three squares in the vertical direction, that is to say, now we have a nine-square grid. Connect the third point in the first row with the first point in the fourth row, and then connect the second point in the first row with the fourth point in the fourth row. The triangle we get is an equilateral triangle.

Hope to adopt-thank you-you can continue to ask me if you don't understand.