What Is a Palindrome? Biden's Inauguration Day Begins 10-Day Run of Rare Dates

Today is President-elect Joe Biden's inauguration day, but there is something else special about the date: January 20, 2021, is a seven-digit palindrome when it is written out as 1/20/2021.

So what is a palindrome? Oxford Languages dictionary defines a palindrome as "a word, phrase, or sequence that reads the same backward as forwards, e.g. madam or nurses run."

The word palindrome was first used in the early 17th century and comes from the Greek palindromos, which means "running back again", from palin meaning "again" and drom- (from dramein "to run"), according to the Oxford Languages Dictionary.

Today's date is an especially rare seven-digit palindrome, but the next nine days will also five-digit palindromes, which are also uncommon.

The 10 upcoming palindrome dates are, including today, 1/20/21, 1/21/21, 1/22/21, 1/23/21, 1/24/21, 1/25/21, 1/26/21, 1/27/21, 1/28/21, and 1/29/21.

We won't see any other palindrome dates this year until December 2021, when we will see eleven palindrome dates: 12/1/21, 12/2/21, 12/3/21, 12/4/21, 12/5/21, 12/6/21, 12/7/21, 12/8/21, 12/9/21, 12/11/21, and 12/22/21.

December 2 will be an even rarer date than today, as it will be an eight-digit palindrome when written out as 12/02/2021.

But just how rare are palindrome dates? In 2011, Aziz Inan, an electrical engineering professor at the University of Portland, calculated that there are just 38 seven and eight-digit palindrome dates in the 21st century.

Inan's calculations consider dates that include the full year, so 2021, rather than simply 21. Inauguration day falls on one of these 38 days, while the next nine days are slightly less rare, but are still uncommon.

From October 2, 2001, (10/02/2001), until September 2, 2090, (09/02/2090), there are 26 seven-digit dates and 12 eight-digit palindrome dates.

Additionally, there will be one palindrome date a year for the next 10 years. These dates will fall on February 20, 2022 (22/02/022), March 20, 2023, (3/20/2023), April 20, 2024 (4/20/2024), May 20, 2025, (5/20/2025), June 20, 2026, (6/20/2026), July 20, 2027, (7/20/2027), August 20, 2028 (8/20/2028), September 20, 2029, (9/20/2029), March 2, 2030 (03/02/2030), and January 30, 2031, (1/30/2031).

Bill Zahner pointed out something else special about today's date and said on Twitter: "1 20 21 is not only a palindrome, but it also has 180-degree rotational symmetry. Just one more reason to appreciate the coming date"

People on Twitter are pointing out the coincidence of the inauguration taking place on a rare date, and journalist Liam Martin pointed out: "In other news, we're in the first day of a string of 10 palindrome dates, and today will be the first inauguration with a palindrome date."

Lawyer and author (and niece of Vice President-elect Kamala Harris) Meena Harris said: "NOBODY TOLD ME TODAY'S DATE IS A PALINDROME," and followed up her tweet by asking: "Someone tell me it's auspicious PLEASE," while Angel Mendoza joked: "bro the inauguration date is a palindrome I [swear to god] Christopher Nolan is a genius."