Divisor 25307

To determine if any number is divisible by 25307, apply the "Sevan Test":

1. If your number ("X") has 6 digits or more, separate the last (smallest) 5 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 6 digits, L = 0 and therefore R = X.
2. Multiply L by 1228 and subtract this from R.
3. Take that result and cross off its final digit (units). Take this new number and subtract 7592 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 25307. That is, your original number is divisible by 25307 if (and only if) Y is. Now that it's much smaller, with basic knowledge of your 25307-times tables, it should be easy to visually see if Y is divisible by 25307. If the Y is still much larger than 25307, the above process can be repeated until it does reduce to within small multiples of 25307.

Easy!