The Cameron-Erdös conjecture

A subset A of integers is said to be sum-free if [email protected]?A for any a,[email protected]?A. Let s(n) be the number of sum-free sets in interval [1,n] of integers. P. Cameron and P. Erdos conjectured that s(n)=O(2^n^/^2). We show that s(n)[email protected]^"02^n^/^2 for even n and s(n)[email protected]^"12^n^/^2 for odd n, where [email protected]^"0,[email protected]^"1 are absolute constants, thereby proving the conjecture.