Palindrome Week: July 10 - July 19, 2017 are all Palindrome Days (m/dd/yy).
A Palindrome Day happens when the day’s date can be read the same way backwards and forwards. The dates are similar to word palindromes in that they are symmetrical.
Because date formats vary from country to country, not all dates that are be considered palindromic in one kind of date format are Palindrome Days in another. For instance, July 10, 2017 or 7-10-2017 is a palindromic date in the m-dd-yyyy format, but isn't if you write the date as mm-dd-yyyy (07-10-2017); as dd-mm-yyyy (10-07-2017) or as yyyy-mm-dd (2017-07-10).
In addition to the format, many people around the world also write the digits on the date differently. For instance, it is common to write only the last two digits of the year – so, 17 instead of 2017. Other such representations include:
- d-m-yyyy or 10-7-2017
- d-m-yy or 10-7-17
- dd-md-yy or 10-07-17
- mm-dd-yy or 07-10-17
Each of these date formats has its own Palindrome Days.
Upcoming Palindrome Daysd-mm-yyyy format
- 6 October 2016 (6-10-2016)
- July 10, 2017 (7-10-2017)
Some Palindrome Dates are Rare
Depending on date formats, palindromic dates can be rare. Aziz S. Inan, an electrical engineering professor at the University of Portland, Portland, U.S.A. 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 Palindrome Day 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 will be 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.
Over a Week of Palindromes
In 2017, people who write their dates in the m-dd-yy format will be treated to 10 consecutive days of palindromic dates. Every day from July 10, 2017 (7-10-17) to July 19, 2017 (7-19-17) will have a palindromic date.
Such back-to-back Palindrome Days in the m-dd-yy format are not that rare. Every year since 2011 have had 10 consecutive Palindrome Days. In 2011, they occurred 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, this will happen in the month of July, in 2018 in August and in 2019 in September.
Notice a pattern here? As long as you write your date in the m-dd-yy format, every century has 9 years with 10 Palindrome Days in a row. These years are always in the second decade of the century. For example, every year between 2011-2019, 2111-2119, and 2211-2219 will have 10 consecutive Palindrome Days. This is true for previous centuries as well.
The month this happens corresponds to the last digit of the year. For instance in 1918, 2018 and 2118, the 8th month of the year, August, will have 10 Palindrome Days. Each of these days will begin on the 11th day of the month and end on the 19th.