Divisor 25439

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

The "Kavan Green Test" for Divisibility by 25439

To determine if any number is divisible by 25439, apply the "Kavan Green Test":

  1. If your number ("X") has 9 digits or more, separate the last (smallest) 8 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 9 digits, L = 0 and therefore R = X.
  2. Multiply L by 709 and subtract this from R.
  3. Take that result and cross off its final digit (units). Take this new number and add 2544 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 25439. That is, your original number is divisible by 25439 if (and only if) Y is. Now that it's much smaller, with basic knowledge of your 25439-times tables, it should be easy to visually see if Y is divisible by 25439. If the Y is still much larger than 25439, the above process can be repeated until it does reduce to within small multiples of 25439.

Easy!