Let D(X) denote the sum of digits of the positive integer X.
For example, D(4007) = 4 + 0 + 0 + 7 = 11.
Take any positive integer X, and let Y = X / D(X). If Y is an integer, we say that Y is the parent of X (and that X is a child of Y).
For example, if X=12 then X / D(X) = 12 / (1+2) = 4, hence 4 is the parent of 12.
Note that multiple numbers can have the same parent. For example, 4 is also the parent of 36, as 36/(3+6) = 36/9 = 4.
We say that a number Y is childless if there is no positive integer X such that Y is the parent of X.
You are given two ints A and B. Find and return the count of all childless numbers that lie between A and B, inclusive.
