arXiv subjects
Publications and source records attributed to Wenguang Zhai.
Let $k\geq 3$ be a fixed integer and $x$ be a large real number. Let $0 0.$ In this paper we show that there exists a constant $1/2\leq \delta_k(\theta)<1$ such that the interval $[x, x + x^{\delta_k(\theta) +\varepsilon} ]$ contains an integer of the form $n_1n_2 \cdots n_k$ such that $|n_j-n^{1/k}|\ll n^{\theta/k} \ (j=1,2, \cdots, k)$. Especially we have $\delta_3(1) = \delta_4(1) = 1/2,$ which improves previous results of Chan.
Let $Δ_1(x;φ)$ denote the error term in the classical Rankin-Selberg problem. In this paper, we consider the higher power moments of $Δ_1(x;φ)$ and derive the asymptotic formulas for 3-rd, 4-th and 5-th power moments, which improve the previous results.
Suppose $a,~b$ are fixed algebraic numbers with $1\leq a<b$. Let $Δ_{a,b}(x)$ be the error term for the number of lattice points in a two-dimensional area $h^ar^b\leq x $ with $h, r$ positive integers. In this paper, we establish an asymptotic formula for the mean square of $Δ_{a,b}(x)$ when $a, b$ are fixed algebraic numbers such that $\dfrac{a}{b}$ is irrational, and improve the error term in the previous asymptotic formula for $a, b$ integers with $(a, b)=1$. Based on these asymptotic formulas, we derive estimates for the sign changes of $Δ_{a,b}(x)$.
Let $\mathcal{P}$ be the set of primes and $\mathbb{N}$ the set of positive integers. Let also $r_1,...,r_t$ be positive real numbers and $R_2(r_1,...,r_t)$ the set of odd integers which can be represented as $$ p+2^{\lfloor k_1^{r_1}\rfloor}+\cdot\cdot\cdot+2^{\lfloor k_t^{r_t}\rfloor}, $$ where $p\in \mathcal{P}$ and $k_1,...,k_t\in\mathbb{N}$. Recently, Chen and Xu proved that the set $R_2(r_1,...,r_t)$ has positive lower asymptotic density, provided that $r_1^{-1}+\cdot\cdot\cdot+r_t^{-1}\ge 1$ and at least one of $r_1,...,r_t$ is an integer. Their result reduces to the famous theorem of Romanoff by taking $t=r_1=1.$ In this note, we remove the unnecessary condition that `{\it at least one of $r_1,...,r_t$ is an integer}'.
Let N be a large enough natural number, A and B be subsets of {N+1, ... , 2N}. In this paper, we prove that there exists integers a, b with a belongs to A, b belongs to B such that ab=P_k^2 + O(P_k^{1-c}), where 0<c<1/2 and P_k denotes an almost-prime with at most k prime factors, counted with multiplicity.
Let $1<c<d$ be two relatively prime integers and $g_{c,d}=cd-c-d$. We confirm, by employing the Hardy--Littlewood method, a 2020 conjecture of Ram\'ırez Alfons\'ın and Skałba which states that $$#\left\{p\le g_{c,d}:p\in \mathcal{P}, ~p=cx+dy,~x,y\in \mathbb{Z}_{\geqslant0}\right\}\sim \frac{1}{2}π\left(g_{c,d}\right) \quad (\text{as}~c\rightarrow\infty),$$ where $\mathcal{P}$ is the set of primes, $\mathbb{Z}_{\geqslant0}$ is the set of nonnegative integers and $π(t)$ denotes the number of primes not exceeding $t$.
Let $π(x;γ_1,γ_2)$ denote the number of primes $p$ with $p\leqslant x$ and $p=\lfloor n^{1/γ_1}_1\rfloor=\lfloor n^{1/γ_2}_2\rfloor$, where $\lfloor t\rfloor$ denotes the integer part of $t\in\mathbb{R}$ and $1/2<γ_2<γ_1<1$ are fixed constants. In this paper, we show that $π(x;γ_1,γ_2)$ holds an asymptotic formula for $21/11<γ_1+γ_2<2$, which constitutes an improvement upon the previous result of Baker [1].
Let $a(n)$ denote the number of non-isomorphic abelian groups with $n$ elements. In 1991 Ivić proved an asymptotic formula of the sum $\sum_{n\leq x} a(n+ a(n)).$ In this paper, we will prove a sharper asymptotic formula for this sum.
Via the MC-algorithm, in this paper we produce seven continued fraction formulae involving products and quotients of three gamma functions with three parameters, and another is an extension of Entry 34 in Chapter 12 of Ramanujan's second notebook. Five of them will be proved rigorously by the Bauer-Muir transformation. A crucial ingredient in the proofs of our five theorems is to employ the Bauer-Muir transformation twice with different nonlinear modifying factors.
In this paper we study Ramanujan sums $c_{\bf m}(\bf n)$, where $ {\bf m}$ and ${\bf n}$ are integral ideals in an arbitrary quadratic number field. We give some new results about the asymptotic behavior of sums of $c_{\bf m}(\bf n)$ over both $ {\bf m}$ and $ {\bf n}$.
Let K be a cubic number field. In this paper, we study the Ramanujan sums c_{J}(I), where I and J are integral ideals in O_{K}. The asymptotic behaviour of sums of c_{J}(I) over both I and J is investigated.
Let $ζ(s)$ and $Z(t)$ be the Riemann zeta function and Hardy's function respectively. We show asymptotic formulas for $\int_0^T Z(t)ζ(1/2+it)dt$ and $\int_0^T Z^2(t) ζ(1/2+it)dt$. Furthermore we derive an upper bound for $\int_0^T Z^3(t)χ^α(1/2+it)dt$ for $-1/2<α<1/2$, where $χ(s)$ is the function which appears in the functional equation of the Riemann zeta function: $ζ(s)=χ(s)ζ(1-s)$.
Let $Z(t)=χ^{-1/2}(1/2+it)ζ(1/2+it)=e^{iθ(t)}ζ(1/2+it)$ be Hardy's function and $g(n)$ be the $n$-th Gram points defined by $θ(g(n))=πn$. Titchmarsh proved that $\sum_{n \leq N} Z(g(2n)) =2N+O(N^{3/4}\log^{3/4}N) $ and $\sum_{n \leq N} Z(g(2n+1)) =-2N+O(N^{3/4}\log^{3/4}N)$. We shall improve the error terms to $O(N^{1/4}\log^{3/4}N \log\log N)$.
Let $d(n; r_1, q_1, r_2, q_2)$ be the number of factorization $n=n_1n_2$ satisfying $n_i\equiv r_i\pmod{q_i}$ ($i=1,2$) and $Δ(x; r_1, q_1, r_2, q_2)$ be the error term of the summatory function of $d(n; r_1, q_1, r_2, q_2)$ with $x\geq (q_1q_2)^{1+\varepsilon}, 1\leq r_i\leq q_i$, and $(r_i, q_i)=1$ ($i=1, 2$). We study the power moments and sign changes of $Δ(x; r_1, q_1, r_2, q_2)$, and prove that for a sufficiently large constant $C$, $Δ(q_1q_2x; r_1, q_1, r_2, q_2)$ changes sign in the interval $[T,T+C\sqrt{T}]$ for any large $T$. Meanwhile, we show that for a small constant $c'$, there exist infinitely many subintervals of length $c'\sqrt{T}\log^{-7}T$ in $[T,2T]$ where $\pm Δ(q_1q_2x; r_1, q_1, r_2, q_2)> c_5x^\frac{1}{4}$ always holds.
We deduce asymptotic formulas for the sums $\sum_{n_1,\ldots,n_r\le x} f(n_1\cdots n_r)$ and $\sum_{n_1,\ldots,n_r\le x} f([n_1\cdots n_r])$, where $r\ge 2$ is a fixed integer, $[n_1,\ldots,n_r]$ stands for the least common multiple of the integers $n_1,\ldots,n_r$ and $f$ is one of the divisor functions $τ_{1,k}(n)$ ($k\ge 1$), $τ^{(e)}(n)$ and $τ^*(n)$. Our formulas refine and generalize a result of Lelechenko (2014). A new generalization of the Busche-Ramanujan identity is also pointed out.
We prove that $$ \int_1^XΔ(x)Δ_3(x)\,dx \ll X^{13/9}\log^{10/3}X, \quad \int_1^XΔ(x)Δ_4(x)\,dx \ll_\varepsilon X^{25/16+\varepsilon}, $$ where $Δ_k(x)$ is the error term in the asymptotic formula for the summatory function of $d_k(n)$, generated by $ζ^k(s)$ ($Δ_2(x) \equiv Δ(x)$). These bounds are sharper than the ones which follow by the Cauchy-Schwarz inequality and mean square results for $Δ_k(x)$. We also obtain the analogues of the above bounds when $\D(x)$ is replaced by $E(x)$, the error term in the mean square formula for $|ζ(1/2+it)|$.
We study a weighted divisor function $\mathop{{\sum}'}\limits_{mn\leq x}\cos(2πmθ_1)\sin(2πnθ_2)$, where $θ_i (0<θ_i<1)$ is a rational number. By connecting it with the divisor problem with congruence conditions, we establish the upper bound, mean-value, mean-square and some power-moments.
Let $S\big(x; \frac{a_1}{q_1}, \frac{a_2}{q_2}\big)=\mathop{{\sum}'}_{mn\leq x} \cos\big(2πm\frac{a_1}{q_1}\big)\sin\big(2πn\frac{a_2}{q_2}\big)$ with $x\geq q_1q_2, 1\leq a_i\leq q_i$, and $(a_i, q_i)=1$ ($i=1, 2$). We study the sign changes of $S\big(x; \frac{a_1}{q_1}, \frac{a_2}{q_2}\big)$, and prove that for a sufficiently large constant $C$, $S\big(x; \frac{a_1}{q_1}, \frac{a_2}{q_2}\big)$ changes sign in the interval $[T,T+C\sqrt{T}]$ for any large $T$. Meanwhile, we show that for a small constant $c'$, there exist infinitely many subintervals of length $c'\sqrt{T}\log^{-7}T$ in $[T,2T]$ where $\pm S\big(t; \frac{a_1}{q_1}, \frac{a_2}{q_2}\big)> c_5 (q_1q_2)^\frac{3}{4}t^\frac{1}{4}$ always holds.