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My opinion: Engineering professor crunches numbers, finds serendipity in the results.

The 2021 calendar of the 21st century is rich with mathematical curiosities. Some of the interesting ones discovered are listed below:

• 2021 is the 21st year of the 21st century.

• The left and right halves of 2021, namely 20 and 21, are consecutive numbers, a property which repeats in four-digit years once every 101 years.

• Additionally, 2021 equals the product of two consecutive prime numbers, 43 and 47. The last year this happened was 1763 (1763 = 41 x 43) and the next one after 2021 will be 2491 (2491 = 47 x 53).

• 2021 contains two full palindrome dates: Jan. 20, 2021, expressed with seven digits as 1/20/2021 and Dec. 2, 2021, expressed with eight digits as 12/02/2021. 2011 is the only other year in this century that has two full palindrome dates: 1/10/2011 and 11/02/2011.

• Moreover, 1/20/2021 and 12/02/2021 are the 14th and 15th of the total 38 full palindrome dates in the 21st century. Coincidentally, the 14th and 15th prime numbers are 43 and 47, and 43 x 47 = 2021.

• If the year part of a date number is expressed in terms of the rightmost two digits of the year, 2021 will offer a total of 22 palindrome dates. Interestingly, eleven of these 22 palindrome dates will occur in January: 1/2/21, 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. The other 11 will occur in December: 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, and 12/11/21. Note that the only other year in the 21st century that also contains 22 palindrome dates is 2011.

• Palindrome date 1/20/21 is also special since 1 + 20 = 21.

• Jan. 9, 2021, expressed as 1/9/2021 consists of three consecutive numbers: 19, 20, and 21.

• April 1, 2021, written as 4/1/2021 is special too since 41 = 20 + 21.

• April 3, 2021, expressed as 4/3/21 consists of sequential numbers 4, 3, 2, and 1, in decreasing order.

• April 20, 2021, expressed as 4/20/2021 is also special since 420 = 20 x 21.

• Aug. 13, 2021, written as 8/13/21 consists of three consecutive Fibonacci numbers: 8, 13, and 21.

• Aug. 19, 2021, expressed as 8/19/2021 is special since 2021 minus 819 equals 1202, the reverse of 2021. The last time this happened was on 9/09/2011 since 2011 - 909 = 1102 and it will happen again on 7/29/2031.

I hope you enjoy the special numerical characteristics of 2021 throughout the year. Happy New Year!

Aziz Inan is a professor teaching in the electrical engineering program of the Donald P. Shiley School of Engineering at University of Portland and he can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..

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