From: Madeleine Yeh <myeh at wap.org>
Subject: [WSFA] Re: 2021 is an interesting number
Date: Mon, 28 Dec 2020 13:06:13 -0500
To: WSFA members <WSFAlist at KeithLynch.net>

That is very interesting.  Thanks for sharing it.

> On Dec 27, 2020, at 4:39 PM, Keith F. Lynch <kfl at KeithLynch.net> wrote:
>
> 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.)
>