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[Richard Guy]

What is the sum of the (proper) unitary divisors of
102016 ?     R.

On Fri, 31 Aug 2001, N. J. A. Sloane wrote:

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> Subject: unitary untouchable numbers
> Date: Fri, 31 Aug 2001 17:35:09 +0200
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> Neil
> I would like to extend the concept of untouchable numbers to the unitary divisors. So the definiton of unitary untouchable numbers should be:
> 
> The numbers n such that us(x)=n has no solution where us(x) is the sum of unitary proper divisors of x.
> 
> With a ubasic code for n<=10^5 I have found the following ones:
> 
> 2 3 4 5 7 374 702 758 926 930 998
> 
> But how I can sure that none of those became solution of us(x)=n for larger values of n (>10^5)?
> 
> Is there any theoretical approach to prove that a number is unitary untouchable?
> 
> Thanks.  Felice
> 
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