Divisor 21481

Prime Number:
Yes!
Divisibility test:
The "Jan Meyer Test"
Test Discovered by:
Matt Parker
Date:
11/11/2024

The "Jan Meyer Test" for Divisibility by 21481

To determine if any number is divisible by 21481, apply the "Jan Meyer 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 Left and Right (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 4993 and subtract this from R.
  3. Take that result and cross off its final digit (units). Take this new number and subtract 2148 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 21481. That is, your original number is divisible by 21481 if (and only if) Y is. Now that it's much smaller, with basic knowledge of your 21481-times tables, it should be easy to visually see if Y is divisible by 21481. If the Y is still much larger than 21481, the above process can be repeated until it does reduce to within small multiples of 21481.

Easy!