| In this thesis, we mainly research on additive complements and complete sequences. The main results are summarized as follows.1. We call two infinite sets A and B of non-negative integers additive complements if their sum contain all sufficiently large integers. Let A(x) and B(x) be the counting functions of A and B. In 2011, Yong-Gao Chen and Jin-Hui Fang proved that for additive complements A = {∑εia2i,εi=0,1,…,a-1},B={∑εja2j-1,εj=0,1,…,a-1},we have,and A(x)B(x)-x≡1 for x = a2k-1.In this thesis, we extend the above result and obtain the following results(Advances in Mathematics (China) ,45(2016), 533-536):(i ) For the above additive complements A and B (taking a = 2), we determine all integers x such that A(x)B(x) - x = 1.(ii ) For any integers a,b with 2≤a≤b, there exist infinite additive complements A,B such that lim sup A(x)B(x)/x=2(ab-1)/ab+a-2,and A(x)B(x)-x =1 for infinitely many positive integers x.2. For a sequence A of nonnegative integers, let P(A) be the set of all integers which can be represented as the sum of distinct terms of A. A sequence A of nonnegative integers is called complete if P(A) contains all sufficiently large integers.For a positive real greatest integer not greater than x and a sequence S= {s1,S2,…} of positive integers. Let Us={α|Sα, is complete} . In 1995,Hegyvari proved that, if sn+1 <γsn for all integers n≥n0,where 1<Y<2,lim(Sn+1-sn)= +∞ and Us≠(?),then μ(Us)>0,where μ(Us) is the Lebesgue measure of Us . In 2013, Yong-Gao Chen and Jin-Hui Fang proved that, if sn+1 < γsn for all integers n≥n0,where 1 <γ≤7/4 , then μ (Us) > 0, In this thesis,we prove that (Acta Math. Hungar.,148 (2016) , 211-221) : the conclusion holds for 1<γ≤(?)=1.898…. |