Submit answers Privacy & Cookies: This site uses cookies. By continuing to use this website, you agree to their use. To find out more, including how to control cookies, see here: Cookie Policy There are currently two active crossnumber competitions: Submit answer for crossnumber #20 (deadline 14 April 2025) Submit answer for crossnumber #21 (deadline 25 September 2025) More from ChalkdustThings to makePlatonic shapes from tube maps, flexagons, and more mathematical craftWhat’s hot and what’s notOptimal Pac-ManGhostbusting with graph theoryReinventing 2DWhat a difference a matrix makesYour social networksHow similar are you to your friends?Art meets mathsClick to share on X (Opens in new window)Click to share on Facebook (Opens in new window)Click to share on Reddit (Opens in new window)Click to share on LinkedIn (Opens in new window)Click to share on Threads (Opens in new window)Click to share on Mastodon (Opens in new window)