Let a1 < a2 < … be an infinite sequence of positive integers and denote by R2 ( n ) the number of solutions of n = ai + aj . P. Erdős and A. Sárközy proved that if g ( n ) is a monotonically increasing arithmetic function with g ( n ) → +∞ and g ( n ) = o ( n (log n ) −2 ) then | R2 ( n ) − g ( n )| = o (√ g ( n )) cannot hold. We will show that for any ɛ > 0, the inequality | R2 ( n ) − g ( n )| ≤ (1 − ɛ )√ g ( n ) cannot hold from a certain point on.
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