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Topic: Can you prove this ?
Replies: 4   Last Post: Jun 30, 1996 7:25 PM

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Mitja Kolsek

Posts: 7
Registered: 12/12/04
Re: Can you prove this ?
Posted: Jun 30, 1996 7:25 PM
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> Some other results.
> n is divisible by 2 : if a_0 is in {0,2,4,6,8}
> n is divisible by 3 : if the sum of the digits is divisible by 3
> n is divisible by 4 : if the last two digits are divisible by 4
> n is divisible by 5 : if a_0 is 0 or 5
> There are a few more.
> Dan

I remember dividing by 11:

n is divisible by 11: if the alternating sum of its digits (a_0 - a_1 + a_2 - a_3 +
...) is divisible by 11

The proof is very similar to that for dividing by 9.

Note that -11, -22, ... are also divisible by 11!

Mitja Kolsek (

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