Let a8e21a39657b844af6aba259342b966e" title="Click to view the MathML source">P denote the set of all primes. P1,P2,P3 are three subsets of a8e21a39657b844af6aba259342b966e" title="Click to view the MathML source">P. Let (i=1,2,3) denote the lower density of Pi in a8e21a39657b844af6aba259342b966e" title="Click to view the MathML source">P, respectively. It is proved that if , , and , then for every sufficiently large odd integer n , there exist pi∈Pi such that n=p1+p2+p3. The condition is the best possible.