From: "Keith F. Lynch" <kfl at KeithLynch.net>
To: WSFA members <WSFAlist at KeithLynch.net>
Subject: [WSFA] 2021 is an interesting number
Date: Sun, 27 Dec 2020 16:39:57 -0500 (EST)

2021 is of course the concatenation of two consecutive integers,
20 and 21.  This last happened in 1920 and will next happen in 2122.

More interestingly, 2021 is the product of two consecutive primes,
43 and 47.  This last happened in 1763 and will next happen in 2491.

2021 is the first year to have both of the above properties.
The next such year will be
794018604377235322848433897872605582794018604377235322848433897872605583,
which is the product of consecutive primes
891077215721081784886888257701070827 and
891077215721081784886888257701070829.

Nobody knows whether there will be a third such year.

(Thanks to Ed Pegg for noticing this.)