Probabilistic construction of small strongly sum-free sets via large Sidon sets

Volume 86 / 2000

Andreas Schoen, Tomasz Srivastav, Anand Baltz Colloquium Mathematicum 86 (2000), 171-176 DOI: 10.4064/cm-86-2-171-176


We give simple randomized algorithms leading to new upper bounds for combinatorial problems of Choi and Erdős: For an arbitrary additive group G let $P_n(G)$ denote the set of all subsets S of G with n elements having the property that 0 is not in S+S. Call a subset A of G admissible with respect to a set S from $P_n(G)$ if the sum of each pair of distinct elements of A lies outside S. Suppose first that S is a subset of the positive integers in the interval [2n,4n). Denote by f(S) the number of elements in a maximum subset of [n,2n) admissible with respect to S. Choi showed that $f(n):=min{|S|+f(S)| S ⊆ [2n,4n)} = On^{3/4})$. We improve this bound to $O(n ln(n))^{2/3})$. Turning to a problem of Erdős, suppose that S is an element of $P_n(G)$, where G is an arbitrary additive group, and denote by h(S) the maximum cardinality of a subset A of S admissible with respect to S. We show $h(n):=min{h(S) | G a group, S ∈ P_n(G)}=O(ln(n))^2)$. Our approach relies on the existence of large Sidon sets.


  • Andreas Schoen
  • Tomasz Srivastav
  • Anand Baltz

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