(*
    Harshad numbers are integers that are divisible by the sum of their
    digits.  For example, 42 / (4 + 2) = 7, so 42 is a Harshad number.
    However, 76 / (7 + 6) is not an integer, so 76 is not.

    ("Harshad" is Sanskrit for "joy giver".)

    Numberphile: 2016502858579884466176 (16:48)
    https://www.youtube.com/watch?v=dgwevhEykWQ

    "There doesn't seem to be anything directly practical you can do
     with Harshad numbers, but you can use them to exercise your
     mathematical muscles" -- and practice writing code in Klein.
*)

function main(n: integer): boolean
    divides(sum_of_digits(n), n)

function sum_of_digits(n: integer): integer
    if n < 10
       then n
       else MOD(n, 10) + sum_of_digits(n/10)

(* 
   recurring utility, from sieve.kln
*)

function divides(a: integer, b: integer): boolean
    MOD(b, a) = 0
   
(*
    utility function from lib.kln
*)

function MOD(m: integer, n: integer ): integer
    m - m/n * n