I have a maths issue which I think can be solved with factorials. But it's a long time since I used them for anything practical and Internet searches just seem to cover simple scenarios.

Anyway, I have all the letters of the alphabet A-Z (just in upper case) and all 10 digits 0-9. So a total of 36 characters in total.

How many 4 characters combinations exist using these 36 characters

e.g. Starting with

AAAA

AAAB

.

.

AAA0

AAA1

.

etc

Any ideas? Is it possible with factorials or am I using the wrong sort of Maths?

Thanks