Divisor 2543

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

The "Christopher Bradfield Test" for Divisibility by 2543

To determine if any number is divisible by 2543, apply the "Christopher Bradfield Test":

  1. If your number ("X") has 5 digits or more, separate the last (smallest) 4 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 5 digits, L = 0 and therefore R = X.
  2. Multiply L by 172 and subtract this from R.
  3. Take that result and cross off its final digit (units). Take this new number and add 763 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 2543. That is, your original number is divisible by 2543 if (and only if) Y is. Now that it's much smaller, with basic knowledge of your 2543-times tables, it should be easy to visually see if Y is divisible by 2543. If the Y is still much larger than 2543, the above process can be repeated until it does reduce to within small multiples of 2543.

Easy!