Lesson 10

Problem. You are registering on a web service that asks you to create a secure password:

• the password must be eight or nine characters long;
• each character of the password must be a letter of the Latin alphabet (lowercase or uppercase) or a digit;
• the password must contain at least one digit.

For example, \(\texttt{A2Jp5eLJg}\), \(\texttt{7m5a5th6}\), and \(\texttt{discr7ete}\) are secure passwords, while \(\texttt{qwertyui}\), \(\texttt{math17}\), \(\texttt{discr-ete}\), and \(\texttt{ghBTrehY}\) are not. How many secure passwords are there?