Sunday, Feb. 2, 2020, is a special date.
If you guessed that’s because of Super Bowl LIV, when the San Francisco 49ers will play against the Kansas City Chiefs — 50 years since the Kansas team won its first Super Bowl title — or Groundhog Day, you’d only be partially correct.
Here’s a hint: Write the full date out in digits using the mm/dd/yyyy format.
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If the date is read from left to right and then from right to left, the sequence remains the same, which makes it a palindrome.
A palindrome is a word, phrase or sequence of numbers that can be read the same way forward and backward. Some other examples of palindromes: “racecar,” “mom,” “dad” and “Red rum, sir, is murder.”
And Sunday’s date is no ordinary palindrome. It’s the rarest kind — an unrepeatable, eight-digit date that can be recognized all over the world, according to University of Portland professor Aziz Inan, who’s been studying numerical palindromes since 2010.
Often palindrome dates in the United States do not align with those in most of the world’s other countries where the dd/mm/yyyy format is more common.
For example, Sept. 10, 2019 (09/10/2019) was a palindrome date in the United States. Countries that write the day before the month, however, would read those digits as Oct. 9, 2019. This means the rest of the world recognized those digits as a palindrome date nearly a month after the United States did.
Sunday’s palindrome date also falls on the 33rd day of the year, with 333 days remaining in the year, Inan noted, which makes this numerical phenomenon just a little freakier.
“02/02/2020 will not repeat next century — in fact, it’ll never repeat in all four-digit years,” Inan said. “That is only one date that occurs in all time, in all the calendar systems.”
From the years 1000 to 9999, there are only 11 such eight-digit “ubiquitous” palindrome dates, as Inan calls them, including Sunday’s:
- 11/11/1111 ----> 909 years ago
- 02/02/2020 ----> Sunday’s date
- 02/12/2121 ----> 101 years later in the 22nd century
The next full palindrome date will occur on Dec. 12, 2121, (12/12/2121) or 101 years from now.
Inan has also compiled a list of seven- and eight-digit palindrome dates in the 21st century. He’s also compiled two lists of palindrome weeks — a 10-day week when all the numbers line up using a m/dd/yy format — one through 2045 and another through 2100.
Inan said that in addition to being a good brain exercise and a way to attract more students to science, technology, engineering and mathematics education, palindromes encourage people to communicate with each other.
“This topic has the power to foster social interaction between people because when somebody finds out that their upcoming birthday is a palindrome date...they share this,” Inan said. “Then people start talking about it.”
CORRECTION (Feb. 1, 2019, 11:04 p.m. ET): An earlier version of this story defined a palindrome week as "a 10-day week when all the numbers line up using a m/dd/yy format that will occur in nine years of every century" and cited the Farmers’ Almanac. Professor Aziz Inan has found that these weeks repeat more than nine times in a century.