Divisor 4871

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

The "Noel Markham Test" for Divisibility by 4871

To determine if any number is divisible by 4871, apply the "Noel Markham Test":

  1. If your number ("X") has 8 digits or more, separate the last (smallest) 7 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 8 digits, L = 0 and therefore R = X.
  2. Multiply L by 163 and subtract this from R.
  3. Take that result and cross off its final digit (units). Take this new number and subtract 487 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 4871. That is, your original number is divisible by 4871 if (and only if) Y is. Now that it's much smaller, with basic knowledge of your 4871-times tables, it should be easy to visually see if Y is divisible by 4871. If the Y is still much larger than 4871, the above process can be repeated until it does reduce to within small multiples of 4871.

Easy!