a fligolo
Solidus.
a prime square
Algebra
Verticies
a washer
Solidus.
A sphere is the correct terminology.
the "number symbol" ( You know 'item # 4.')
A hemisphere would be the correct name.
Prime factors
hash
Octalthorp. Note that, in Britain the '#' sign is called 'hash' and isn't used as the number sign - we write 'No.' for number.
a prime square
Algebra
the largest number
The word could possibly be integer. That's the mathematical name for a whole number.
When you add a number to itself, you are multiplying it by 2. The usual term for this is you are doubling the number.