Divisor 9391

To determine if any number is divisible by 9391, apply the "Eagris Test":

1. If your number ("X") has 5 digits or more, separate the last (smallest) 4 digits from the rest. This makes two smaller numbers, call them L^eft and R^ight (note: don't add in trailing zeros to L). If there are fewer than 5 digits, L = 0 and therefore R = X.
2. Multiply L by 609 and add to R.
3. Take that result and cross off its final digit (units). Take this new number and subtract 939 times the digit you just crossed off. Call this final result "Y".
4. Y will be much smaller than X, but we have preserved divisibility by 9391. That is, your original number is divisible by 9391 if (and only if) Y is. Now that it's much smaller, with basic knowledge of your 9391-times tables, it should be easy to visually see if Y is divisible by 9391. If the Y is still much larger than 9391, the above process can be repeated until it does reduce to within small multiples of 9391.

Easy!