This may only work for the U.S., so my apologies to the rest of my global brethren if it doesn't work for you. Our phone numbers have a three digit prefix called an area code followed by three more numbers and then four more after that. An example would be (239) 555-7779.
Here is a math phenomenon that will get you thinking.
1. Grab a calculator. (You won't be able to do this one in your head)
2. Key in the first three digits of your phone number (NOT the area code)
3. Multiply by 80
4. Add 1
5. Multiply by 250
6. Add the last 4 digits of your phone number
7. Add the last 4 digits of your phone number again.
8. Subtract 250
9. Divide number by 2
Do you recognize the answer???
