Divisor 20939

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

The "Fredrik Hendeberg Test" for Divisibility by 20939

To determine if any number is divisible by 20939, apply the "Fredrik Hendeberg 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 4664 and subtract this from R.
  3. Take that result and cross off its final digit (units). Take this new number and add 2094 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 20939. That is, your original number is divisible by 20939 if (and only if) Y is. Now that it's much smaller, with basic knowledge of your 20939-times tables, it should be easy to visually see if Y is divisible by 20939. If the Y is still much larger than 20939, the above process can be repeated until it does reduce to within small multiples of 20939.

Easy!