<p>The average of the <i>k</i>-fold divisor function <Equation ID="Equ26"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1029_Article_Equ26.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="321" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned} d_k(n) {:}{=} \# \{(a_1, \dots , a_k) \in {\mathbb {Z}}_{\geqslant 0}^k: a_1 \cdots a_k = n\} \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <msub> <mi>d</mi> <mi>k</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mo>=</mo> <mo>#</mo> <mrow> <mo stretchy="false">{</mo> <mrow> <mo stretchy="false">(</mo> <msub> <mi>a</mi> <mn>1</mn> </msub> <mo>,</mo> <mo>⋯</mo> <mo>,</mo> <msub> <mi>a</mi> <mi>k</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo>∈</mo> <msubsup> <mi mathvariant="double-struck">Z</mi> <mrow> <mo>⩾</mo> <mn>0</mn> </mrow> <mi>k</mi> </msubsup> <mo>:</mo> <msub> <mi>a</mi> <mn>1</mn> </msub> <mo>⋯</mo> <msub> <mi>a</mi> <mi>k</mi> </msub> <mo>=</mo> <mi>n</mi> <mo stretchy="false">}</mo> </mrow> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>over arithmetic progressions has been widely studied. The Beatty sequence <Equation ID="Equ27"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1029_Article_Equ27.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="152" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned} {\mathcal {B}}_{\alpha ,\beta } {:}{=} \left( \lfloor \alpha n+\beta \rfloor \right) _{n=1}^\infty \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <msub> <mi mathvariant="script">B</mi> <mrow> <mi>α</mi> <mo>,</mo> <mi>β</mi> </mrow> </msub> <mo>:</mo> <mo>=</mo> <msubsup> <mfenced close=")" open="("> <mo>⌊</mo> <mi>α</mi> <mi>n</mi> <mo>+</mo> <mi>β</mi> <mo>⌋</mo> </mfenced> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>∞</mi> </msubsup> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>is considered as a generalization of arithmetic progressions. In this article, we estimate the average of the <i>k</i>-fold divisor function over Beatty sequences in arithmetic progressions, namely <Equation ID="Equ28"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1029_Article_Equ28.gif" Format="GIF" Height="74" Rendition="HTML" Resolution="72" Type="Linedraw" Width="164" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned} \sum _{\begin{array}{c} {n \leqslant x, n\in {\mathcal {B}}_{\alpha ,\beta }}\\ {n\equiv a (\textrm{mod}\, r) } \end{array}} d_{k}(n). \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <munder> <mo>∑</mo> <mrow> <mtable> <mtr> <mtd> <mrow> <mi>n</mi> <mo>⩽</mo> <mi>x</mi> <mo>,</mo> <mi>n</mi> <mo>∈</mo> <msub> <mi mathvariant="script">B</mi> <mrow> <mi>α</mi> <mo>,</mo> <mi>β</mi> </mrow> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mrow> <mi>n</mi> <mo>≡</mo> <mi>a</mi> <mo stretchy="false">(</mo> <mtext>mod</mtext> <mspace width="0.166667em" /> <mi>r</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </mtd> </mtr> </mtable> </mrow> </munder> <msub> <mi>d</mi> <mi>k</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo stretchy="false">)</mo> </mrow> <mo>.</mo> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>We obtain the main term and give bounds on the error terms for different <i>k</i> and a refinement for <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1029_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(k \geqslant 5\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>⩾</mo> <mn>5</mn> </mrow> </math></EquationSource> </InlineEquation> when <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1029_Article_IEq2.gif" Format="GIF" Height="10" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\(\alpha \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>α</mi> </math></EquationSource> </InlineEquation> is of finite type. This covers the previous results related to the average of divisor functions over Beatty sequences.</p>

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The k-fold divisor function over Beatty sequences

  • Jinyun Qi,
  • Victor Zhenyu Guo

摘要

The average of the k-fold divisor function \(\begin{aligned} d_k(n) {:}{=} \# \{(a_1, \dots , a_k) \in {\mathbb {Z}}_{\geqslant 0}^k: a_1 \cdots a_k = n\} \end{aligned}\) d k ( n ) : = # { ( a 1 , , a k ) Z 0 k : a 1 a k = n } over arithmetic progressions has been widely studied. The Beatty sequence \(\begin{aligned} {\mathcal {B}}_{\alpha ,\beta } {:}{=} \left( \lfloor \alpha n+\beta \rfloor \right) _{n=1}^\infty \end{aligned}\) B α , β : = α n + β n = 1 is considered as a generalization of arithmetic progressions. In this article, we estimate the average of the k-fold divisor function over Beatty sequences in arithmetic progressions, namely \(\begin{aligned} \sum _{\begin{array}{c} {n \leqslant x, n\in {\mathcal {B}}_{\alpha ,\beta }}\\ {n\equiv a (\textrm{mod}\, r) } \end{array}} d_{k}(n). \end{aligned}\) n x , n B α , β n a ( mod r ) d k ( n ) . We obtain the main term and give bounds on the error terms for different k and a refinement for \(k \geqslant 5\) k 5 when \(\alpha \) α is of finite type. This covers the previous results related to the average of divisor functions over Beatty sequences.