function eifelerRegelAppliesToNumber(number) {
        number = parseInt(number, 10);
        if (isNaN(number)) {
            return false;
        }
        if (number < 0) {
            // Negative Number --> always true
            return true;
        } else if (number < 10) {
            // Only 1 digit
            if (4 <= number && number <= 7) {
                return true;
            }
            return false;
        } else if (number < 100) {
            // 2 digits
            var lastDigit = number % 10, firstDigit = number / 10;
            if (lastDigit === 0) {
                return eifelerRegelAppliesToNumber(firstDigit);
            }
            return eifelerRegelAppliesToNumber(lastDigit);
        } else if (number < 10000) {
            // 3 or 4 digits --> recursively check first digit
            while (number >= 10) {
                number = number / 10;
            }
            return eifelerRegelAppliesToNumber(number);
        } else {
            // Anything larger than 4 digits: recursively check first n-3 digits
            number = number / 1000;
            return eifelerRegelAppliesToNumber(number);
        }
    }
Returns true if the word before the given number loses the '-n' ending.
e.g. 'an 10 Deeg' but 'a 5 Deeg'

@param number {integer}
@returns {boolean}