Write all composite numbers between $1 \& 20$.

The number $17 \& 71$ are prime numbers. Both have the same digits $1 \& 7$. Find at least one more such pair of prime numbers below $100$.

Write twin primes between $1 \& 50$.

Which of the following are pairs of co-primes? 

$\left(2,3\right), \left(3,9\right), \left(9,11\right), \left(11,13\right), \left(13,15\right), \left(15,18\right), \left(18,21\right)$.

Make a list of all odd numbers between $1 \& 100$ which are not prime numbers.

Write the following as the sum of two prime numbers.

$36$

Write the following as the sum of two prime numbers.

$45$

Write the following as the sum of two prime numbers.

$80$

Write the following as the sum of two prime numbers.

$32$