<p>We investigate the following two-parameter class of real sequences <Equation ID="Equa"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3340_Article_Equa.gif" Format="GIF" Height="36" Rendition="HTML" Resolution="72" Type="Linedraw" Width="227" /> </MediaObject> <EquationSource Format="MATHML"><math> <msubsup> <mi>a</mi> <mi>n</mi> <mrow> <mo stretchy="false">(</mo> <mi>p</mi> <mo stretchy="false">)</mo> </mrow> </msubsup> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> <mo>=</mo> <msup> <mrow> <mo maxsize="3.8ex" minsize="3.8ex" stretchy="true">(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mi>α</mi> <mi>n</mi> </mfrac> <mo maxsize="3.8ex" minsize="3.8ex" stretchy="true">)</mo> </mrow> <mrow> <mi>n</mi> <mo>+</mo> <mi>p</mi> </mrow> </msup> <mo>,</mo> <mspace width="1em" /> <mi>n</mi> <mo>∈</mo> <mi mathvariant="double-struck">N</mi> <mo>,</mo> </math></EquationSource> <EquationSource Format="TEX">\( a_{n}^{(p)}(\alpha )=\Big(1+\frac{\alpha }{n}\Big)^{n+p},\quad n\in { \mathbb{N}}, \)</EquationSource> </Equation> where <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3340_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>p</mi> <mo>≥</mo> <mn>0</mn> </math></EquationSource> <EquationSource Format="TEX">$p\ge 0$</EquationSource> </InlineEquation> and <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3340_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="57" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>α</mi> <mo>&gt;</mo> <mo>−</mo> <mn>1</mn> </math></EquationSource> <EquationSource Format="TEX">$\alpha &gt;-1$</EquationSource> </InlineEquation>. In the case <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3340_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>p</mi> <mo>≥</mo> <mn>0</mn> </math></EquationSource> <EquationSource Format="TEX">$p\ge 0$</EquationSource> </InlineEquation> and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3340_Article_IEq4.gif" Format="GIF" Height="13" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>α</mi> <mo>&gt;</mo> <mn>0</mn> </math></EquationSource> <EquationSource Format="TEX">$\alpha &gt;0$</EquationSource> </InlineEquation>, we give some sufficient and necessary conditions such that <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3340_Article_IEq5.gif" Format="GIF" Height="24" Rendition="HTML" Resolution="72" Type="Linedraw" Width="89" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <msubsup> <mi>a</mi> <mi>n</mi> <mrow> <mo stretchy="false">(</mo> <mi>p</mi> <mo stretchy="false">)</mo> </mrow> </msubsup> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> <mo>≤</mo> <msup> <mi>e</mi> <mi>α</mi> </msup> </math></EquationSource> <EquationSource Format="TEX">$a_{n}^{(p)}(\alpha )\le e^{\alpha }$</EquationSource> </InlineEquation> for every <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3340_Article_IEq6.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="47" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>n</mi> <mo>≥</mo> <mi>k</mi> </math></EquationSource> <EquationSource Format="TEX">$n\ge k$</EquationSource> </InlineEquation>, for each fixed <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3340_Article_IEq7.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="44" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>k</mi> <mo>∈</mo> <mi mathvariant="double-struck">N</mi> </math></EquationSource> <EquationSource Format="TEX">$k\in {\mathbb{N}}$</EquationSource> </InlineEquation>, some sufficient and necessary conditions such that <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3340_Article_IEq8.gif" Format="GIF" Height="24" Rendition="HTML" Resolution="72" Type="Linedraw" Width="88" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <msup> <mi>e</mi> <mi>α</mi> </msup> <mo>≤</mo> <msubsup> <mi>a</mi> <mi>n</mi> <mrow> <mo stretchy="false">(</mo> <mi>p</mi> <mo stretchy="false">)</mo> </mrow> </msubsup> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> </math></EquationSource> <EquationSource Format="TEX">$e^{\alpha }\le a_{n}^{(p)}(\alpha )$</EquationSource> </InlineEquation> for every <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3340_Article_IEq9.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="45" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <mi>n</mi> <mo>∈</mo> <mi mathvariant="double-struck">N</mi> </math></EquationSource> <EquationSource Format="TEX">$n\in {\mathbb{N}}$</EquationSource> </InlineEquation>, and some sufficient conditions so that the sequence strictly increasingly converges to <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13660_2025_3340_Article_IEq10.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="MATHML"><math> <msup> <mi>e</mi> <mi>α</mi> </msup> </math></EquationSource> <EquationSource Format="TEX">$e^{\alpha }$</EquationSource> </InlineEquation>, improving some results in the literature. Beside this, we give several remarks and comments related to the class of sequences and functions which are used in this investigation.</p>

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On a two-parameter class of sequences converging to a power of the base of the natural logarithm

  • Stevo Stević

摘要

We investigate the following two-parameter class of real sequences a n ( p ) ( α ) = ( 1 + α n ) n + p , n N , \( a_{n}^{(p)}(\alpha )=\Big(1+\frac{\alpha }{n}\Big)^{n+p},\quad n\in { \mathbb{N}}, \) where p 0 $p\ge 0$ and α > 1 $\alpha >-1$ . In the case p 0 $p\ge 0$ and α > 0 $\alpha >0$ , we give some sufficient and necessary conditions such that a n ( p ) ( α ) e α $a_{n}^{(p)}(\alpha )\le e^{\alpha }$ for every n k $n\ge k$ , for each fixed k N $k\in {\mathbb{N}}$ , some sufficient and necessary conditions such that e α a n ( p ) ( α ) $e^{\alpha }\le a_{n}^{(p)}(\alpha )$ for every n N $n\in {\mathbb{N}}$ , and some sufficient conditions so that the sequence strictly increasingly converges to e α $e^{\alpha }$ , improving some results in the literature. Beside this, we give several remarks and comments related to the class of sequences and functions which are used in this investigation.