Gap-free floor conjecture for semiprime subset sums

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Let NN be a positive integer, let PNP_N be the product of the primes at most NN, and let L2(N)L^2(N) denote the set of subset sums of the corresponding semiprime unit-fraction contributions. Define

γN=inf⁡{γ:[γPN, σ2(N)−γPN]∩Z⊆L2(N)}.\gamma_N=\inf\{\gamma:[\gamma P_N,\,\sigma^2(N)-\gamma P_N]\cap\mathbb{Z}\subseteq L^2(N)\}.

Gap-free floor conjecture.

γN→0as N→∞.\gamma_N\to0\quad\text{as }N\to\infty.

This conjecture asserts that the semiprime subset sums become gap-free throughout the bulk of the interval [0,σ2(N)][0,\sigma^2(N)], apart from a vanishing proportion near its two ends. It identifies the remaining open core of the ω=2\omega=2 case of the Erdős–Graham problem; the supplied source does not state a resolution.

References

Primary source

Shisheng Li, “Every natural number is a sum of distinct semiprime unit fractions”, arXiv:2606.15159 (2026).

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