My dad sent this in an email:
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?
Hey! That's my ex-girlfriend's prison number!
Posted by: David Richards at November 18, 2005 01:45 PMThat's pretty clever. You're essentially multiplying your prefix by 10,000. Then, you add the remaining 4 numbers. The middle steps kind of serve to mask this.
Posted by: Chris at November 18, 2005 01:48 PMChris nailed it. If n = 3-digit prefix and m = last 4 digits, the equation is:
phone# = ( ( ( n*80 ) + 1 ) * 250 + 2*m - 250 ) / 2
Or, skipping the +1 (which necessitates removing the -250) and simplifing a little:
phone# = ( n*80*250 + 2*m ) / 2
Again:
phone# = ( 20000*n + 2*m ) / 2,
or
phone# = 10000*prefix + extension
And I thought I had too much time on my hands!
Sheesh, guys! ;-)
Posted by: Clifton D. Healy at November 18, 2005 04:19 PMSo that's why it doesn't work with my 6-digit UK phone number.
Posted by: Dave at November 20, 2005 11:52 AM