Additive combinatorics | Sumsets

Sum-free set

In additive combinatorics and number theory, a subset A of an abelian group G is said to be sum-free if the sumset A⊕A is disjoint from A. In other words, A is sum-free if the equation has no solution with . For example, the set of odd numbers is a sum-free subset of the integers, and the set {N+1, ..., 2N} forms a large sum-free subset of the set {1,...,2N}. Fermat's Last Theorem is the statement that, for a given integer n > 2, the set of all nonzero nth powers of the integers is a sum-free subset. Some basic questions that have been asked about sum-free sets are: * How many sum-free subsets of {1, ..., N} are there, for an integer N? Ben Green has shown that the answer is , as predicted by the Cameron–Erdős conjecture (see Sloane's OEIS: ). * How many sum-free sets does an abelian group G contain? * What is the size of the largest sum-free set that an abelian group G contains? A sum-free set is said to be maximal if it is not a proper subset of another sum-free set. Let be defined by is the largest number such that any subset of with size n has a sum-free subset of size k. The function is subadditive, and by Fekete subadditivity lemma, exists. Erdos proved that , and conjectured that it is exact("P. Erdős, "Extremal problems in number theory", Matematika, 11:2 (1967), 98–105; Proc. Sympos. Pure Math., Vol. VIII, 1965, 181–189"). This is proved in. (Wikipedia).

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Related pages

Additive combinatorics | Additive number theory | Cameron–Erdős conjecture | Fermat's Last Theorem | Sumset | Subadditivity | Abelian group