qed (12. 732)

A once in a century event, at least for jurisdictions observing the MM-DD-YY format (see also), today—rendered as 9/16/25—illustrates the Pythagorean Theorem—that is, a²+b²=c² or three-squared plus four-squared equals five squared or the unit measures of the shorter vertices of any right triangle yield its hypotenuse. As a bonus, the full year, 2025 (see above), is the square of forty-five.  More auspicious dates with numerical properties at the links above.