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Old 08-26-2016, 11:13 AM
Folly Folly is offline
Join Date: Aug 2004
Location: Chicago! (no more burbs)
Posts: 1,969
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.