How to Easily Identify Any 2-Digit Prime Number

From a channel Lumen includes in full: Combo Class (Domotro) teaches unusual corners of number theory, combinatorics and maths history in a free-wheeling classroom format, with real mathematical content behind the chaotic style.

A 15-minute video from Combo Class's catalogue; the title names its topic.

Video by Combo Class, played through YouTube's embedded player.