A Harshad number is an integer divisible by the sum of its digits.
The calculator returns either a list of Harshad numbers up to the limit input by the user or checks to see whether the number input is a Harshad number.
The limit is based solely on your patience. A limit of 1,000,000 takes about a 4 seconds to calculate. But scrolling through the list of 95,248 Harshad numbers takes significantly longer.