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The present question is tangentially related to this earlier one.

My question here is:

Does $2r - \sigma(r)$ divide $\sigma(r)$ if $r$ is deficient-perfect?

Recall that a positive integer $x$ is deficient-perfect if $x$ satisfies $D(x) \mid x$, where $D(x) = 2x - \sigma(x)$ is the deficiency of $x$ and $\sigma(x)$ is the sum of divisors of $x$.

My conjecture is that the answer is NO.

MY ATTEMPT

Suppose that $r$ is deficient-perfect.

This means that $2r - \sigma(r) = D(r) \mid r$, so that $r$ can be written in the form $$r = {R_1}D(r),$$ for some (positive) integer $R_1$.

This implies that $$r(2{R_1} - 1) = {R_1}\sigma(r).$$

Assume to the contrary that $D(r) \mid \sigma(r)$. Then it follows that $$\sigma(r) = {R_2}D(r) = {R_2}(2r - \sigma(r))$$ for some (positive) integer $R_2$.

This implies that $$r(2{R_1} - 1) = {R_1}\sigma(r) = {R_1}{R_2}D(r) = {R_1}{R_2}(2r - \sigma(r))$$ from which we obtain $${R_1}{R_2}\sigma(r) = 2r{R_1}{R_2} - r(2{R_1} - 1).$$ Dividing through by ${R_1}{R_2}$, we get $$\sigma(r) = r\Bigg(2 - \bigg(\frac{2{R_1} - 1}{R_1 R_2}\bigg)\Bigg).$$

Alas, this is where I get stuck.

1 Answers1

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If $2x-\sigma(x)$ divides $x$ then it divides $2x$ and $2x-\sigma(x)$ thus it divides $2x-(2x-\sigma(x)) = \sigma(x)$

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