input: Write a function to determine if a number provided by the user is prime or not. If the number is prime, return True, otherwise return False.
  assert is_prime(17)==True
  assert is_prime(4)==False
  assert is_prime(1)==False
  assert is_prime(2)==True
  assert is_prime(3)==True
output: def is_prime(n):
      if n <= 1:
          return False
      if n == 2:
          return True
      if n % 2 == 0:
          return False
      for i in range(3, int(n**0.5) + 1, 2):
          if n % i == 0:
              return False
      return True