View Single Post
Old 08-26-2016, 12:13 PM
Folly Folly is offline
Join Date: Aug 2004
Location: Chicago! (no more burbs)
Posts: 1,897
The second one is a variation or consequence I guess of 'casting out nines'.

The digits, even when reversed, will add to the same number and the result when subtracted will always be divisible by 9.