code: function getDerivative(num) {
  	var derivative = 1;
  	while (num != 0) {
  		derivative += num % 7;
  		num = Math.floor(num / 7);
  	}
  	return derivative;
  }
docs: Gets a derivative of a number by repeatedly dividing it by 7 and adding the
  remainders together.  It's useful to base decisions on a derivative rather
  than the wordObj's current numeric, as it avoids making the same decisions
  around the same phonetics.
  
  @param {number} num A number from which a derivative should be calculated
  @returns {number} The derivative.