# A Simple Proof of a 400-Year Old Theorem about Numbers

## Sometimes the simplest proofs give the best insights into how mathematicians think

Fermat’s Little Theorem is a beautiful number-theoretic result which states that, for any integer *a* and any prime number *p*, *aᵖ﹣a *is divisible by *p*. For example, if *a* = 4 and *p = 3* then *aᵖ﹣a = *60 which is divisible by 3.