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9/29/29 – Math lovers share an affinity for palindromic calendar dates, which can be read symmetrically backward and forward in their numerical date format. But Sept. 29, 1929 must have been a banner day for number crunchers as it's one of the few dates that have more than one palindromic form: 9/29, 9/29/29 and 9/29/1929.
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Pi Day -- This year this date was extra special, as 2015 stretched the symbolic March 14 celebration out a little longer to 3.1415. If you want to take it even further, 9:26 a.m. (or p.m. if you're not observing military time) on Saturday, March 14, 2015, marked 3.1415926, or the first eight digits of pi.
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1961 – Few can say they've lived in a perfect year, but for those around in 1961, congratulations. Those alive in 1961 did something no one else did in the last century, and that no one else will do for 4,000 years: read your year upside down or right side up. While there's no particular date that stands out as odd that year, the fact that this calendar anomaly won't occur again until the year 6009 may lend credence to the notion that the 60s were a time of new perspectives.
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12/31/99 – The Prince song "1999" enjoyed new life as the world amped up massive celebrations in preparation for the new millennium. There was widespread fear that the world’s data storage systems would fail, since many computers were programmed to handle only two-digit year dates. People thought the "Y2K bug" would shut down the world's computers and data storage systems. It didn't.
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06/06/06 – The Bible's Book of Revelation calls 666 the number of the beast, so more than a few eyebrows were raised as June 6, 2006 approached. In the days prior, the evangelical Raptureready.com website said the day had a "rapture index" of 156, suggesting that it was "fasten your seatbelts" time, the Associated Press reported. Others cashed in -- moviemakers released the remake of the horror film "The Omen" on the date.