<p>The generalised weak Schur number, denoted by <i>WS</i>(<i>k</i>,&#xa0;<i>l</i>), is defined to be the largest positive integer <i>n</i> such that the set <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1123_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="134" /> </InlineMediaObject> <EquationSource Format="TEX">\([n]=\{1,2,\dots ,n\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">[</mo> <mi>n</mi> <mo stretchy="false">]</mo> <mo>=</mo> <mo stretchy="false">{</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo>,</mo> <mo>⋯</mo> <mo>,</mo> <mi>n</mi> <mo stretchy="false">}</mo> </mrow> </math></EquationSource> </InlineEquation> can be partitioned into <i>k</i> disjoint subsets that do not contain solutions to the equation <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1123_Article_IEq2.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="124" /> </InlineMediaObject> <EquationSource Format="TEX">\(x_1+\dots +x_l=y\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>+</mo> <mo>⋯</mo> <mo>+</mo> <msub> <mi>x</mi> <mi>l</mi> </msub> <mo>=</mo> <mi>y</mi> </mrow> </math></EquationSource> </InlineEquation> where the numbers <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1123_Article_IEq3.gif" Format="GIF" Height="12" Rendition="HTML" Resolution="72" Type="Linedraw" Width="87" /> </InlineMediaObject> <EquationSource Format="TEX">\(x_1,\dots ,x_l,y\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>,</mo> <mo>⋯</mo> <mo>,</mo> <msub> <mi>x</mi> <mi>l</mi> </msub> <mo>,</mo> <mi>y</mi> </mrow> </math></EquationSource> </InlineEquation> are pairwise distinct. The generalised weak Schur number modulo <i>m</i>, denoted by <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1123_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="76" /> </InlineMediaObject> <EquationSource Format="TEX">\(WS_m(k,l)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>W</mi> <msub> <mi>S</mi> <mi>m</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>k</mi> <mo>,</mo> <mi>l</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, is similarly defined with equality swapped for congruence modulo <i>m</i>. In 2023, Ahmed, Boza, Revuelta, and Sanz found new exact values and lowers bounds for <i>WS</i>(<i>k</i>,&#xa0;<i>l</i>). However, since 2013, the values of <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1123_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="76" /> </InlineMediaObject> <EquationSource Format="TEX">\(WS_m(k,l)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>W</mi> <msub> <mi>S</mi> <mi>m</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>k</mi> <mo>,</mo> <mi>l</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> are only known for <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1123_Article_IEq6.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="77" /> </InlineMediaObject> <EquationSource Format="TEX">\(m=1,2,3\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>m</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo>,</mo> <mn>3</mn> </mrow> </math></EquationSource> </InlineEquation>. In this paper, we determine new exact values and bounds for <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1123_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="76" /> </InlineMediaObject> <EquationSource Format="TEX">\(WS_m(k,l)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>W</mi> <msub> <mi>S</mi> <mi>m</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>k</mi> <mo>,</mo> <mi>l</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> for general values of <i>m</i>. In particular, we establish that <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1123_Article_IEq8.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="195" /> </InlineMediaObject> <EquationSource Format="TEX">\(kl \le WS_m(k,l) \le klm-1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mi>l</mi> <mo>≤</mo> <mi>W</mi> <msub> <mi>S</mi> <mi>m</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>k</mi> <mo>,</mo> <mi>l</mi> <mo stretchy="false">)</mo> </mrow> <mo>≤</mo> <mi>k</mi> <mi>l</mi> <mi>m</mi> <mo>-</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation> and found the exact value of <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1123_Article_IEq9.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="74" /> </InlineMediaObject> <EquationSource Format="TEX">\(WS_m(1,l)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>W</mi> <msub> <mi>S</mi> <mi>m</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo>,</mo> <mi>l</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> when <i>l</i> is large enough. Furthermore, when <i>m</i> is a prime and <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1123_Article_IEq10.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="109" /> </InlineMediaObject> <EquationSource Format="TEX">\(l\not \equiv 1\pmod m\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>l</mi> <mo>≢</mo> <mn>1</mn> <mspace width="4.44443pt" /> <mo stretchy="false">(</mo> <mo>mod</mo> <mspace width="0.277778em" /> <mi>m</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, we also determine the exact values of <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11139_2025_1123_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="76" /> </InlineMediaObject> <EquationSource Format="TEX">\(WS_m(k,l)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>W</mi> <msub> <mi>S</mi> <mi>m</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>k</mi> <mo>,</mo> <mi>l</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> under the conditions that <i>l</i> and <i>k</i> are large.</p>

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Modular generalisations of weak Schur numbers

  • Jourdan D’orville,
  • Kai An Sim,
  • Kok Bin Wong,
  • Chee Kit Ho

摘要

The generalised weak Schur number, denoted by WS(kl), is defined to be the largest positive integer n such that the set \([n]=\{1,2,\dots ,n\}\) [ n ] = { 1 , 2 , , n } can be partitioned into k disjoint subsets that do not contain solutions to the equation \(x_1+\dots +x_l=y\) x 1 + + x l = y where the numbers \(x_1,\dots ,x_l,y\) x 1 , , x l , y are pairwise distinct. The generalised weak Schur number modulo m, denoted by \(WS_m(k,l)\) W S m ( k , l ) , is similarly defined with equality swapped for congruence modulo m. In 2023, Ahmed, Boza, Revuelta, and Sanz found new exact values and lowers bounds for WS(kl). However, since 2013, the values of \(WS_m(k,l)\) W S m ( k , l ) are only known for \(m=1,2,3\) m = 1 , 2 , 3 . In this paper, we determine new exact values and bounds for \(WS_m(k,l)\) W S m ( k , l ) for general values of m. In particular, we establish that \(kl \le WS_m(k,l) \le klm-1\) k l W S m ( k , l ) k l m - 1 and found the exact value of \(WS_m(1,l)\) W S m ( 1 , l ) when l is large enough. Furthermore, when m is a prime and \(l\not \equiv 1\pmod m\) l 1 ( mod m ) , we also determine the exact values of \(WS_m(k,l)\) W S m ( k , l ) under the conditions that l and k are large.