<p>Let <i>K</i> be an imaginary quadratic field with fundamental discriminant <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(d_K\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>d</mi> <mi>K</mi> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(C(\tau )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>C</mi> <mo stretchy="false">(</mo> <mi>τ</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> be the Ramanujan’s cubic continued fraction. We prove in this note that if <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(d_K\equiv 5\pmod {8}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>d</mi> <mi>K</mi> </msub> <mo>≡</mo> <mn>5</mn> <mspace width="4.44443pt" /> <mrow> <mo stretchy="false">(</mo> <mo>mod</mo> <mspace width="0.277778em" /> <mn>8</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, then the values <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(2^{2/3}C(\tau ), 2^{1/3}C(\tau /2), 2^{2/3}C(\tau /3)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mn>2</mn> <mrow> <mn>2</mn> <mo stretchy="false">/</mo> <mn>3</mn> </mrow> </msup> <mi>C</mi> <mrow> <mo stretchy="false">(</mo> <mi>τ</mi> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> <msup> <mn>2</mn> <mrow> <mn>1</mn> <mo stretchy="false">/</mo> <mn>3</mn> </mrow> </msup> <mi>C</mi> <mrow> <mo stretchy="false">(</mo> <mi>τ</mi> <mo stretchy="false">/</mo> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> <msup> <mn>2</mn> <mrow> <mn>2</mn> <mo stretchy="false">/</mo> <mn>3</mn> </mrow> </msup> <mi>C</mi> <mrow> <mo stretchy="false">(</mo> <mi>τ</mi> <mo stretchy="false">/</mo> <mn>3</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(2^{1/3}C(\tau /6)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mn>2</mn> <mrow> <mn>1</mn> <mo stretchy="false">/</mo> <mn>3</mn> </mrow> </msup> <mi>C</mi> <mrow> <mo stretchy="false">(</mo> <mi>τ</mi> <mo stretchy="false">/</mo> <mn>6</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> are algebraic units all some <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\tau \in K\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>τ</mi> <mo>∈</mo> <mi>K</mi> </mrow> </math></EquationSource> </InlineEquation> in the complex upper half-plane <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\mathbb {H}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="double-struck">H</mi> </math></EquationSource> </InlineEquation>. We also construct ray class fields modulo 2 over <i>K</i> using <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(C^3(\tau )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>C</mi> <mn>3</mn> </msup> <mrow> <mo stretchy="false">(</mo> <mi>τ</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> under certain conditions on <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\tau \in K\cap \mathbb {H}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>τ</mi> <mo>∈</mo> <mi>K</mi> <mo>∩</mo> <mi mathvariant="double-struck">H</mi> </mrow> </math></EquationSource> </InlineEquation>. Our results complement those of Cho, Koo, and Park and, more recently, of Akkarapakam and Morton on the generators of ray class fields over <i>K</i> involving some values of <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(C(\tau )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>C</mi> <mo stretchy="false">(</mo> <mi>τ</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>.</p>

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Remarks on The Values of the Cubic Continued Fraction

  • Russelle Guadalupe

摘要

Let K be an imaginary quadratic field with fundamental discriminant \(d_K\) d K and \(C(\tau )\) C ( τ ) be the Ramanujan’s cubic continued fraction. We prove in this note that if \(d_K\equiv 5\pmod {8}\) d K 5 ( mod 8 ) , then the values \(2^{2/3}C(\tau ), 2^{1/3}C(\tau /2), 2^{2/3}C(\tau /3)\) 2 2 / 3 C ( τ ) , 2 1 / 3 C ( τ / 2 ) , 2 2 / 3 C ( τ / 3 ) , and \(2^{1/3}C(\tau /6)\) 2 1 / 3 C ( τ / 6 ) are algebraic units all some \(\tau \in K\) τ K in the complex upper half-plane \(\mathbb {H}\) H . We also construct ray class fields modulo 2 over K using \(C^3(\tau )\) C 3 ( τ ) under certain conditions on \(\tau \in K\cap \mathbb {H}\) τ K H . Our results complement those of Cho, Koo, and Park and, more recently, of Akkarapakam and Morton on the generators of ray class fields over K involving some values of \(C(\tau )\) C ( τ ) .