Summary: 1. Fermat's Little Theorem: if p is prime, then b^p = b (mod p) for all integers b. i.e. b^p - b is always a multiple of p. 8^3-8 = 512-8 = 504 = 168 x 3. 2. Is the inverse true? Does b^n - b = 0 (mod n) mean that n is prime? No. Sometimes n is non-prime (like n=561, divisible by 3). We call these n, Carmichael numbers. 3. Okay, so these numbers exist. How common are they? For primes we know they're common.…
Thanks for this. I find articles like this super hard to read due to the mixing of the topic and all the "back ground". It does sometimes feel like it's only there to bulk out the article.
The writer can fix the article, or let every reader fix it in his mind.