The “periodic table of finite simple groups”, by Ivan Andrus: https://irandrus.wordpress.com/2012/06/17/the-periodic-table-of-finite-simple-groups/ To do: make an equally useful and silly picture, but with improved organization (no reason to split the classical groups across both sides, except to make it look more like the chemical periodic table).
Digital timestamp: Need to certify that you have a proof of the Riemann hypothesis (or whatever) today, but not yet ready to go public? http://www.itconsult.co.uk/stamper.htm (and then don’t email it to me)
