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Re: Can you prove this ?
Posted:
Jun 30, 1996 7:25 PM


> 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 (mitja.kolsek@unimb.si)



