I am aware of a few interesting mathematical tricks...
The Sum of Nine: Any number multiplied by nine will have its digits up to nine.
Example:
8*9 = 72 | 7+2=9
16*9 = 144 | 1+4+4=9
256*9 = 2304 | 2+3+0+4=9
16384*9 = 147456 | 1+4+7+4+5+6= 27 | 2+7=9
This works with ANY whole number multiplied by 9.
I am also aware of a equation that will enable you to determine what day of the week a particular date will fall on...
January 20th 1886 = XXXday..
I don' know the specifics and hope that maybe one of our resident mathemeticans will have a clue.
Anyways, if use any little math tricks and are willing to share, I know that I'd like to hear them.
-SF