Square root day is a humorous holiday celebrated on dates where the day and the month are both the square root of the last two digits in the current year. For example, the last square root day was February 2, 2004 (2/2/04), and the next square root day will be March 3, 2009 (3/3/09). The final square root day of the century will occur on September 9, 2081.
One suggested way of celebrating the holiday is by eating square radishes, or other root vegetables cut into shapes with square cross sections.
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(Well, what do you know? I never knew such “humorous” celebration exists until today.)