public static int generateModulus(final boolean odd) {
        final int[] primes = new int[] {2, 3, 5, 7, 11, 13, 17, 19, 23, 29,
            31, 37, 41, 43, 47};

        // start on index 0, 1, 2, 3
        final int startingIndex = randInt(odd ? 1 : 0, 3);  
        // end max. on index 14, 10, 7, 5
        int maxFinishingIndex = 13 - startingIndex * 3;     
        if (startingIndex == 0 || startingIndex == 3)
            ++maxFinishingIndex;
        final int finishingIndex = randInt(startingIndex + 1, maxFinishingIndex);

        return primes[startingIndex] * primes[finishingIndex];
    }