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An April Fool's Math Quiz

I can't say what this has to do with the environment, but apparently today's date, April 1, 2009, has the dubious distinction of being a "square date." That is, when you write out the date's digits as a number, it has whole numbers for square roots (4,012,009 = 2,003 x 2,003). As the University of Portland's Aziz Inan points out, square dates are incredibly rare—we'll only see 100 in this millennium—which makes it all the more remarkable that 2009 had two of them (the other was on March 5, since 3,052,009 = 1,747 x 1,747). Enjoy it while it lasts, I suppose, since the next square date doesn't pop up until February 26, 2016.

--Bradford Plumer