Trivia
Subject:
Puzzler -- PINsAlex Y
A bank assigns 4-digit PINs to their customers' ATM cards. They use all the digits (including leading zeros). But fearing that some customers may be superstitious, they make it a practice never to have "13" appear in the PIN. I.e., "4153" is a legitimate PIN, but "4135" is not.
How many unique PINs can they assign using with this restriction in place?
