This week, many Americans celebrated “palindrome week” -- a string of days in which the date is the same whether written forward or backward. For example, 9/10/19 is "91/01/9" backward -- if you take out the slashes, then the numbers are in the exact same order.

However, this is only true when the dates are written in the American method and referring to it as a “week” is a misnomer, but we’ll get to all of that in a second.

Some news outlets, as well as Twitter moments, called this the last palindrome week of the century. Is there really no other instance of this for the next 81 years?

For the next 10 days, the date will be the same written backward as it is forward.

### THE QUESTION

Is this the last palindrome week for nearly a century?

No, it’s not even the last one for the next two years.

### WHAT WE FOUND

The next palindrome week begins as recently as January of 2021. January 20 will start it off with the date of 1/20/21 and the palindrome dating will continue until 1/29/21. There will be another palindrome week later that year in December when the date becomes 12/1/21 and will continue until 12/9/21. There will also be palindrome days on 12/11/21 and 12/22/21.

That makes this palindrome week the last of the decade, but not the last of the century. There will be several other palindrome weeks throughout the next decade.

This occasion happens because of the American date-writing method of MM/DD/YY. In other parts of the world where the date is written DD/MM/YY, consecutive days where the date is a palindrome never occur because the front part of the date changes everyday.

Even with the American method, you have to write the date out in very specific ways to create the palindrome effect. Writing today’s date as 9/13/19 would a palindrome but writing it as 09/13/19 would not. Likewise, writing the date as 12/01/21 in December of 2021’s palindrome week would make it so the date is no longer a palindrome. A whole different wrench is thrown into the mix when all four numbers are written out in the year, regardless if it’s MM/DD/YYYY or DD/MM/YYYY.

“Palindrome week” also doesn’t fit the definition of a week in anyway. This year’s palindrome week started on a Tuesday and it lasts for 10 days rather than seven.

However, if we use the same criteria of palindrome week that was used to classify the current string of dates as palindrome week -- that is 10 consecutive days in which a M/D/YY date is written the same forward as it is backward -- then there will be several more this century.