Divisor 28283

To determine if any number is divisible by 28283, apply this test:

1. If your number ("X") has 10 digits or more, separate the last (smallest) 9 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 10 digits, L = 0 and therefore R = X.
2. Multiply L by 2031 and subtract this from R.
3. Take that result and cross off its final digit (units). Take this new number and add 8485 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 28283. That is, your original number is divisible by 28283 if (and only if) Y is. Now that it's much smaller, with basic knowledge of your 28283-times tables, it should be easy to visually see if Y is divisible by 28283. If the Y is still much larger than 28283, the above process can be repeated until it does reduce to within small multiples of 28283.

Easy!