Last night, on our way to the fireworks in Antwerp, we walked by this definition of prime numbers:
“The numbers, only divisible by $1$ and itself are: $2,3$ and every number before or after a multiple of $6$, without their squares or products.” (Peter Wynen)
True enough.
And a lot more user-friendly than: the generators of the multiplicative monoid of all natural numbers which are $\pm 1$ modulo $6$ are the prime numbers, except for $2$ and $3$.
I wish you a 2018 full of math (and artistic) pleasures.