Representation functions of sequences in additive number theory
Representation functions of sequences in additive number theory
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DOI:
10.1090/s0002-9939-1978-0503522-6
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发表时间:
1978
期刊:
影响因子:
--
通讯作者:
M. Nathanson
中科院分区:
文献类型:
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作者:
M. Nathanson
Let ? be a set of nonnegative integers, and let r2f(n) denote the number of representations of n in the form n = ai + aj with ai, aj E d. The set 6 is periodic if a^E E implies a + m E El for some m > I and all a > N. It is proved that if E is not periodic, then for every set ' +# E there exist infinitely many n such that r2(n) # r2s(n). Moreover, all pairs of periodic sets El and S are constructed that satisfy r2(n) = r2s(n) for all but finitely many n. Let 6l be a set of nonnegative integers. Let r^(n) denote the number of representations of n as a sum of h elements of 6d. If f(z) = E-a EqZa is the generating function for 6', then f(z)h = 0?=Orha(n)z n. Let rd(n) denote the number of representations of n as a sum of an arbitrary number of elements of 61. If 0 M C, then rg(n) = XO Ir d(n) is finite for all n. Representation functions have been studied by various authors [147]. In this note I consider the question: To what extent do the sequences r, (n) and rd(n) determine the set ? I shall prove that if D and '9i3 are sets of nonnegative integers such that r^ (n) = r^ (n) for some h > 1 and all n > 0, or if ro(n) = rB(n) for all n > 0, then 6, = fi3. However, there do exist sets 6! and 'iJ such that 9,(n) = r4(n) for all sufficiently large n, but Cl7 :#3 . All such pairs of sets 6C and 93 will be constructed explicitly. An infinite set 6C of integers is called periodic if there exist integers m > 1 and N such that a E cT implies a + m E 6S for all a > N. It will be shown that if the set C is not periodic, then for every set 0J =# CT we must have r(n) 7# r4(n) for infinitely many n. THEOREM 1. Let d( and 93 be sets of nonnegative integers, and let rh(n) and rhs(n) denote the number of representations of n as a sum of h elements of C and (M, respectively. If rh(n) = rhB(n) for all n > 0, then (E = (3. PROOF. If rhd(n) = rh4(n) for all n > 0, then