Find the number of 7-digit (base-10) numbers, such that each of the digits 1,2,3,4,5 must appear in the number (once or more).
Clearly, no leading zeros.
(In reply to analytic solution, subject to error
Heaven forbid, I would never complain that somebody elected to tackle a problem analytically. But I am curious why you didn't write a computer program. Feeling whimsical? I seems to me that you could code this one with one hand tied behind your back. Is it just that it would be too easy?