Did you know there are 4 different digits that square numbers can never end in? In this bonus video, let me explain why certain numbers can or can't be a square's last digit in base ten, and how this applies to other bases. Technically, this concept is known as the "quadratic non-residues mod 10". For an older video of mine involving quadratic residues (the opposite of quadratic non-residues here), check out this episode on my https://www.youtube.com/channel/UC_3urRDzQbfOh2eh1fYfnLQ channel: https://www.youtube.com/watch?v=hH89nUGd6DU And here's a new Combo Class episode about an interesting base some computers use instead of binary: https://www.youtube.com/watch?v=yfQVL0_POKg Also check out the new short (a visualization of the "difference of squares" identity) I just put out on my https://www.youtube.com/channel/UC_3urRDzQbfOh2eh1fYfnLQ channel:    • Shorts   Links to some other recent videos are below: My "May Announcement" about my computer incident, changes to my upcoming "shorts", etc. : https://www.youtube.com/watch?v=2qZsw8UWt-w Latest Combo Class episode: https://www.youtube.com/watch?v=eEYnI14_Q1A The short I put out on the Combo Class channel recently:    • Shorts   The short I put out on this channel recently: (this one might have notified subscribers but most aren't going too)    • These Are The Only Numbers With This ...   Special thanks to my Patreon supporters: Max, George Carozzi, Peter Offut, Tybie Fitzhugh, Henry Spencer, Mitch Harding, YbabFlow, Joseph Rissler, Plenty W, Quinn Moyer, Julius 420, Philip Rogers, Ilmori Fajt, Brandon, August Taub, Ira Sanborn, Matthew Chudleigh, Cornelis Van Der Bent, Craig Butz, Mark S, Thorbjorn M H, Mathias Ermatinger, Edward Clarke, and Christopher Masto, Joshua S, Joost Doesberg, Adam, Chris Reisenbichler, Stan Seibert, Izeck, Beugul, OmegaRogue, Florian, William Hawkes, Michael Friemann, Claudio Fanelli, and Julian Zassenhaus. (To join that list of people supporting this channel, and get cool bonus content, check out the Combo Class Patreon at https://www.patreon.com/comboclass) This video was filmed by Carlo Trappenberg. Links: Main channel: null Patreon: https://www.patreon.com/comboclass Discord: https://discord.gg/cHHvDcPPuc Subreddit: https://www.reddit.com/r/comboClass/ If you have any extra clocks/dice/etc., here's my private mailbox address (not my home address). If you're going to send anything, please watch this short video first: https://www.youtube.com/watch?v=_-gSvbvO8W4 Domotro 1442 A Walnut Street, Box # 401 Berkeley, CA 94709 If you want to reach out to possibly collaborate or help with Combo Class somehow, my email is: combouniversity (at) gmail (dot) com Combo Class, taught by Domotro, is a crazy educational show where you can have fun learning rare things about math, science, language, and more! This is the channel for Domotro's Combo Class bonus videos, shorts, and livestreams - make sure you're also subscribed to the main @ComboClass channel where the main episodes go! DISCLAIMER: any use of fire, tools, or other science experiments in this series is always done in a safe and professional way. Do not try to copy any actions you see in this series yourself.