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arXiv · 2606.20057

On the asymptotic density of the ordered pairs $(a,b)$ of positive integers such that $\gcd(ab,a+b)=\gcd(a,b)$

Steve Fan·László Tóth
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Abstract

Consider the arithmetic function of two variables $f(a,b)= \gcd(ab,a+b)/\gcd(a,b)$, investigated in a recent preprint. We deduce asymptotic formulas for sums of the form $\sum_{a,b\le x} h(f(a,b))$, where $h$ belongs to a certain class of arithmetic functions. In particular, we obtain an asymptotic formula for the number of ordered pairs $(a,b)\in {\Bbb N}^2$ such that $a,b\le x$ and $f(a,b)=m$, where $m\in {\Bbb N}$ is fixed. This shows that in the case $m=1$ the corresponding density is the quadratic class number constant $C= \prod_p (1-1/(p^2(p+1))) \doteq 0.881513$.

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Steve Fan, László Tóth. 2026-06-18. On the asymptotic density of the ordered pairs $(a,b)$ of positive integers such that $\gcd(ab,a+b)=\gcd(a,b)$. https://arxiv.org/abs/2606.20057

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