A number n is a Harshad (also called Niven) number if it is divisible by the sum of its digits. For example, 666 is divisible by 6 + 6 + 6, so it is a Harshad number.
Write a function to determine whether the given number is a Harshad number.
is_harshad(209) ➞ True
is_harshad(41) ➞ False
is_harshad(12255) ➞ True
N/A