A neat way of separating a deck of playing cards into red and black piles is the one-two trick: move the pack from one hand to the other, taking clumps of one colour or two colours alternately.
Takes at most four runs through to completely separate the colours in a 52-card deck. (Why?)

Mad Abel is a card game for wo or more players which involves multiplication in the finite group of your choice: read.somethingorotherwhatever.

A Mastodon instance for maths people. The kind of people who make $\pi z^2 \times a$ jokes.

Use $ and $ for inline LaTeX, and $ and $ for display mode.