I posted this article on CodeProject.com a while back.   The problem it solves, comes up from time to time.    I wrote it, as part of  the online donations site, for SunnyBrook Hospital Foundation.  The system accepted the donation, and would automatically generate a PDF of the official tax receipt for Charitable donations.

I also posted code for load-testing, in the ‘comments’ section on that page.

https://www.codeproject.com/articles/Flexible-numbering-sequences-in-T-SQL