Madam, I'm Adam.
You've likely heard that palindrome sentence, which is spelled the same way forwards and backwards. But palindrome dates seem to spark a lot of curiosity as well.
Palindrome dates, by their very nature, only occur in the early centuries of a millennium. There will be 36 of them during this millennium, with the last one occurring on Sept. 22, 2290. The next one after that won't be until Oct. 3, 3001.
In 2020, for example, only one day is a palindrome in the m-dd-yyyy format:
- Feb. 2, 2020: 2-02-2020
Palindromic dates also depend on how a date is formatted, which can vary depending on where you live. If you spell out the date in a different way, like the mm-dd-yy format — which is common in the United States — there are two more dates in 2020:
- Feb. 11, 2020: 02-11-20
- Feb. 22, 2020: 02-22-20
(It's worth noting that for safety reasons, it's better to spell out the year 2020 to discourage forgers from tinkering with your documents, explains USA Today.)
Aziz S. Inan, an electrical engineering professor at the University of Portland, has calculated that when dates are written in the mm-dd-yyyy format, palindrome days typically occur only in the first few centuries of each millennium, according to timeanddate.com. The first example of a palindrome in the current millennium (Jan. 1, 2001 to Dec. 31, 3000) was Oct. 2, 2001 (10-02-2001) and the last one will be Sept. 22, 2290 (09-22-2290).
For countries that use the dd-mm-yyyy format, there are 29 palindrome days in the current century. The first was 10 February 2001 (10-02-2001). The last will be a leap day: 29 February 2092 (29-02-2092), which will also be the last palindrome day of the 21st century.
Although it might seem like strings of palindrome dates — or palindrome weeks — might be rare, Inan says that's hardly the case.
Since 2011, every year has had 10 consecutive palindrome days. In 2011, they started on Jan. 10 (1-10-11 through 1-19-11), for example, and in 2012, another string started on Feb. 10 (2-10-12 through 2-19-12). In 2019, it happened in September.
In the m-dd-yy format, every century has nine years with 10 consecutive palindrome days. Timeanddate.com points out that they're always in the second decade of the century. Every year between 2011-2019, 2111-2119, and 2211-2219 will have 10 palindrome days in a row.
But palindrome dates aren't the only way that calendar number geeks — I mean enthusiasts — get their thrills.
Among other patterns, there are repeating dates (1/11/11 = 11111), repeating sequences (10/31/03 = 103 103), and sequential dates (8/9/10 = 8,9,10; and if you start with the time of 12:34:56.7, you get 1, 2, 3, 4, 5, 6, 7, 8, 9, 10).
Editor's note: This story has been updated since it was published in October 2012.