number-theory / Number Theory

Erdős Problem #856

Let $k\geq 3$ and $f_k(N)$ be the maximum of $\sum_{n\in A}\frac{1}{n}$ over all $A\subseteq\{1,\ldots,N\}$ containing no $k$ subsets with the same pairwise least common multiple. Estimate $f_k(N)$. The claimed answer: $f_k(N)=(\log N)^{\gamma_k+o(1)}$, where $\gamma_k$ is a weighted generalization of the Tang-Zhang sunflower capacity.

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number-theoryApr 15, 2026Significance 10/100Registry: unreviewed

Erdős Problem #856

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Identifies the exponent as a variational sunflower-capacity constant, sharpening the Tang-Zhang bounds; the value of that constant itself remains open, as does site acceptance

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Let $k\geq 3$ and $f_k(N)$ be the maximum of $\sum_{n\in A}\frac{1}{n}$ over all $A\subseteq\{1,\ldots,N\}$ containing no $k$ subsets with the same pairwise least common multiple. Estimate $f_k(N)$. The claimed answer: $f_k(N)=(\log N)^{\gamma_k+o(1)}$, where $\gamma_k$ is a weighted generalization of the Tang-Zhang sunflower capacity.

Identifies the exponent as a variational sunflower-capacity constant, sharpening the Tang-Zhang bounds; the value of that constant itself remains open, as does site acceptance

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