Divisor 11903

To determine if any number is divisible by 11903, apply the "Harmelodic Test":

1. If your number ("X") has 7 digits or more, separate the last (smallest) 6 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 7 digits, L = 0 and therefore R = X.
2. Multiply L by 148 and add to R.
3. Take that result and cross off its final digit (units). Take this new number and add 3571 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 11903. That is, your original number is divisible by 11903 if (and only if) Y is. Now that it's much smaller, with basic knowledge of your 11903-times tables, it should be easy to visually see if Y is divisible by 11903. If the Y is still much larger than 11903, the above process can be repeated until it does reduce to within small multiples of 11903.

Easy!