From Wikipedia: A Dudeney number is a positive integer that is a perfect cube such that the sum of its decimal digits is equal to the cube root of the number.
Write a function that returns true if a number is a Dudeney number and false otherwise.
Assume all numbers are of base 10.
If a number is negative, assume that only the leading digit carries the negative sign e.g. -4913 -> (-4+9+1+3)^3