Numbers

     When my mind still needs to think, but I have run out of words, I resort to numbers.   I know there must be  a logical answer to this, but I can't think of what it is:    when you are going through the times tables, why do the numbers in the 9 set alone  add up to 9?    9x7=63, with the 6 and the 3 adding up to 9, as do all the 2 numbers you multiply in the 9 times table.  It's not true of 1 through 8; what's so special about 9?