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sum_divisors=sum_antidivisors

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  • djbroadhurst
    Max B asked ... The excluding is unnecessary, since 1 is not an anti-divisor. For what it s worth, I reckon that the sequence, up to 10^5, is 11 22 33 65
    Message 1 of 2 , Sep 2, 2002
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      "Max B" asked

      > What would
      > "n such that the sum of divisors of
      > n = sum of the anti-divisors of n
      > excluding 1)" be?

      The "excluding" is unnecessary, since
      1 is not an anti-divisor.

      For what it's worth, I reckon that
      the sequence, up to 10^5, is

      11
      22
      33
      65
      82
      117
      218
      483
      508
      537
      6430
      21541
      Good bye!
    • djbroadhurst
      Off-list, Max B asked for my code for this exercise. For what it s worth, this was it: {SA(n)=local(o);o=n;while(o%2==0,o=o/2);
      Message 2 of 2 , Sep 2, 2002
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        Off-list, Max B asked for my code for this exercise.

        For what it's worth, this was it:

        {SA(n)=local(o);o=n;while(o%2==0,o=o/2);
        sigma(2*n+1,1)+sigma(2*n-1,1)+sigma(o,1)*2*n/o-6*n-2}
        for(n=1,10^5,if(sigma(n,1)==SA(n),print(n)))

        But I did no sanity check!

        David
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