For security purposes I regularly change my six-digit passcode for internet banking. I always choose a code that is made up of three different two-digit square numbers (i.e. square numbers between 10 and 99), with the sixth digit the same as the first digit

Which two digits never appear in any of my passcodes?

How many different passcodes can I use?

The sum of the six digits of my
current passcode is also a square number. What is my current passcode?