Print pyramid digit question?

Well m is the variable which holds the numbers which are displayed one by one on the console.

The reason why m is being decremented by 2 is to reduce the numbers which are displayed on the right hand side of the pyramid by 2 so that they are symmetric with those on the left hand side.

Before the RHS is printed, m will be 1 more than the number in the middle column.

So, if you didn't decrement m by 2, then the second row of the pyramid would read:

2 3 4

and the third row would read:

3 4 5 6 5

By reducing m by 2, the second row is now:

2 3 2

and the third row is:

3 4 5 4 3