A prime number is a number which does not have any divisors other than \(1\) and itself.
By convention we do not refer to \(0\) or \(1\) as prime numbers.
Divisors must be smaller than the number. As a result it is easy to identify early prime numbers, as we can try to divide by all preceding numbers.
\([2, 3 5, 7, 11, 13,...]\)
Composite numbers are numbers that are made up through the multiplication of other numbers.
They are not prime.
This functions counts numbers up to \(n\) which are relatively prime
eg for 10 we have \(1\), \(3\), \(7\), \(9\).
So \(\phi (10)=4\)
Given a set of nautral numbers, the Frobenius number is the biggest number which can’t be made as linear combination of the set.