CB>Start with a number, cross off the last digit, subtract twice that 
CB>deleted last digit from the remaining portion of the number.  Repeat 
CB>the process.  as needed.  if the remainder is 0 or any other 
CB>multiple of 7, the number is divisible by 7.
CB>Example...
CB> 2156  Start with this number, cross off the six, leaving...
CB> 215  but now subtract 2 x 6 (12)...
CB> -12
CB> ___
CB> 203  Repeat the process - drop the 3...
CB> 20   and double the 3 (6) to subtract...
CB> -6
CB> __
CB>  14  remainder is 14, a multiple of 7, so 2156 is divisible by 7.
Ok... Now WHY does this work?  Or the other rules for that
matter?                                ;-)
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 * MR/2 2.26 * "OS/2 is destined to be the most important OS" - Bill Gates
--- PCBoard (R) v15.3 (OS/2) 2
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