You do not need any lisinsing. Nor do you need any licensing. However, numeracy and literacy - being able to work with numbers and related concepts and being able to present arguments coherently are necessary.
Everything you need WWW.Google.com is there
Yes, Pythagoras is a mathematician.
Mathematician
mathematician
pythagorus was a mathematician
Mathematician is 'Mathematiker'
mathematician
Yes, George Boole was a mathematician.
A mathematician can be a engineer, an astronaut or a electrician.
mathematician
yes Mary was a mathematician
Euler was a prolific mathematician who answered a large number of questions. You will need to be more specific.