input: Write a function named is_prime that determines if a given number is prime or not. Return True if the number is prime, otherwise return False.
  assert is_prime(17)==True
  assert is_prime(2)==True
  assert is_prime(1)==False
  assert is_prime(4)==False
output: def is_prime(n):
      if n <= 1:
          return False
      for i in range(2, int(n**0.5) + 1):
          if n % i == 0:
              return False
      return True