Special Calendar Dates
The Gregorian calendar is full of dates that, when written in a numerical format, form unique and interesting mathematical patterns. These patterns are considered by some people as having special significance.
Numerical date patterns are not very rare—most dates in the calendar can be written in a way to form a mathematical pattern. There are some date patterns, however, that are rare and occur only a few times in a century.
Different Date Formats
People around the world use different date order formats to write down the numerical form of calendar dates. Some of these common formats are:
- Month/Day/Year - MM/DD/YYYY - Mostly used in North America.
- Day/Month/Year - DD/MM/YYYY - Mostly used in the European languages.
- Year/Month/Day - YYYY/MM/DD - Mostly used in the Chinese language.
In addition to having different date formats, people in many countries also write the digits in the date differently. For example, it is very common in many places to write only the last two digits of the year – 16 instead of 2016. Other such different ways of writing the digits for a date include:
- D/M/YYYY or 1/1/2019
- D/M/YY or 1/1/19
- DD/MM/YYYY or 01/01/2019
- DD/MM/YY or 01/01/19
- MM/DD/YYYY or 01/01/2019
- MM/DD/YY or 01/01/19
Sequential dates occur when the digits on the date are in an increasing or decreasing sequence.
Sequential dates depend on the format used to write the date - a date can only be sequential if only the last two digits of the year (YY) are used and tend to happen in the early part of a century. For example, if you write your date in the MM/DD/YY format, the last sequential date of the century for you is December 13, 2014 or 12/13/14. The next such alignment of digits in a date will happen 89 years later on January 2, 2103 or 01/02/03. Those of you who write their dates in the DD/MM/YY format, the last such sequential date for the century occurred on December 11, 2013 or 11/12/13.
Palindrome dates are dates in which the digits that can be read the same way backward or forward. Because of the varying ways in which dates are written around the world, a palindromic date in one date format may not be considered a palindrome in another. In the MM/DD/YYYY and the DD/MM/YYY format, the next palindromic date will be February 2, 2020 or 02/02/2020 or 02022020.
Dates with digits that repeat have become more common since 2001.
Repeating dates can occur in any of the date formats mentioned above. For example:
- In the DD-MM-YYYY format: October 20, 2010 or 20-10-2010 can also be written as 2010-2010
- In the MM-DD-YY format: October 31, 2003 or 10-31-2003, can also be written as 103-103