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Palindrome Day

A Palindrome Day happens when the day’s date can be read the same way backward and forward. The dates are similar to word palindromes in that they are symmetrical.

Palindrome

'BOB' is a palindrome.

'BOB' is feeling lucky on his Palindrome Day. Palindrome dates read the same way backward and forward.

Because date formats vary from country to country, not all dates that are considered palindromic in one kind of date format are Palindrome Days in another. For instance, September 10, 2019 or 9-10-19 is only a palindromic date in the m-dd-yy format, but it isn't if you write the date as mm-dd-yyyy (09-10-2019); as dd-mm-yyyy (10-09-2019) or as yyyy-mm-dd (2019-09-10).

Palindrome Week 2019

In September of 2019, every day for 10 consecutive days was a palindrome in the m-dd-yy format, which is common in the United States:

  • 9-10-19
  • 9-11-19
  • 9-12-19
  • 9-13-19
  • 9-14-19
  • 9-15-19
  • 9-16-19
  • 9-17-19
  • 9-18-19
  • 9-19-19

Different Digits

In addition to the format, many people around the world also write the digits of the date differently. For instance, it is common to write only the last two digits of the year – so, 19 instead of 2019. Other date representations include:

  • d-m-yyyy or 10-9-2019
  • d-m-yy or 10-9-19
  • dd-md-yy or 10-09-19
  • mm-dd-yy or 09-10-19

Each of these date formats has its own Palindrome Days.

Some Palindrome Dates are Rare

Illustration image
Some dates are palindromic.
Whether a date is palindromic or not depends on how it is written.

Depending on date formats, palindromic dates can be rare. Aziz S. Inan, an electrical engineering professor at the University of Portland, has calculated that in the mm-dd-yyyy format, Palindrome Days tend to occur only in the first few centuries of each millennium (1000 years). The last palindromic date in the second millennium (years 1001 to 2000) in this format was August 31, 1380 or 08-31-1380.

According to Dr. Inan, in the mm-dd-yyyy format, the first of 36 Palindrome Days in the current millennium (January 1, 2001 to December 31, 3000) was October 2, 2001 (10-02-2001) and the last such day will be September 22, 2290 (09-22-2290).

There are 12 Palindrome Days in the 21st century in the mm-dd-yyyy format. The first one was on October 2, 2001 (10-02-2001) and the last one will be on September 2, 2090 (09-02-2090).

In 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 is a special one – it's a leap day! 29 February 2092 (29-02-2092) will be the last Palindrome Day of the 21st century.

Palindrome Weeks

The back-to-back Palindrome Days in the m-dd-yy format are not that rare. For example, every year since 2011 has had 10 consecutive Palindrome Days.

The month in which this happens always corresponds to the last digit of the year. In 2011, the Palindrome Week ran from January 10, 2011 (1-10-11) to January 19, 2011 (1-19-11). In 2012, the same sequence of dates occurred in February. In 2017, it happened in July, in 2018 in August and in 2019, it happens in September.

Topics: Dates, Calendar, Fun

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