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

Let x=the first 3 digits of your phone number
Let y=the last 4 digits of your phone number

Do the math:
1. 80x
2. 80x + 1
3. 250(80x + 1) = 20000x + 250
4. 20000x + 250 + y
5. 20000x + 250 + 2y
6. 20000x 2y
7 10000x + y
Let phone number = 123-4567
then x=123, y=4567
10000x + y = 1230000 + 4567 = 1234567.