My work phone number is a typical US 10 digits number. In addition:
- a) My office is in the same area code as Stanford University.
- b) The area code appears twice in my phone number
- c) The number of the beast doesn’t appear in my phone number.
- d) An even number can only be in an even-numbered position if the value of that number is also its position (the leftmost digit is in position 1; 0 is an even number).
- e) The number of occurrences of non-zero numbers is always less than the value of the number.
- f) The answer uses as few different numbers as possible to meet all these conditions. For example, if 123-123-1231 and 123-412-3412 both met all the constraints above (which they obviously don’t), then the answer would be 123-123-1231 because it only uses the numbers 1, 2 and 3, while the other uses an additional number (4).
Asking your Oracle-employed brother-in-law to look me up in the employee phone book is considered cheating…
[UPDATED 2009/1/23: Clarified last bullet with an example, based on reader feedback.]