input: Write a python function to find all prime numbers up to a given number n.
  assert find_all_primes(10) == [2, 3, 5, 7]
  assert find_all_primes(20) == [2, 3, 5, 7, 11, 13, 17, 19]
  assert find_all_primes(5) == [2, 3, 5]
output: def find_all_primes(n):
      def is_prime(x):
          if x < 2:
              return False
          for i in range(2, int(x**0.5) + 1):
              if x % i == 0:
                  return False
          return True
  
      return [i for i in range(2, n+1) if is_prime(i)]