input: Write a function to determine if a number input by the user is a prime number. The function should return True if the number is prime and False otherwise. If the number is less than 2, the function should also return False.
  
  assert is_prime(2)==True
  assert is_prime(17)==True
  assert is_prime(1)==False
  assert is_prime(9)==False
  assert is_prime(-5)==False
output: def is_prime(n):
      if n < 2:
          return False
      for i in range(2, int(n**0.5) + 1):
          if n % i == 0:
              return False
      return True