Number fun.

As a schoolkid, I was always fascinated by the story of the "Indestructible Nine".  If you take any number and multiply it by 9, the digits of the answer will always add up to 9.  Think of a number - 5,726 say.  Multiply it by 9.  The answer is 51,534. Add those digits together: 5+1+5+3+4 = 18.  Do the same again: 1+8 = 9.  And there you are - works for any number you care to think of.  The other thing I remember our maths teacher amazing us with was that 111,111,111 multiplied by 111,111,111 comes to 12,345,678,987,654,321!