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Binary quadratic forms and Eichler orders

Montserrat Alsina (2005)

Journal de Théorie des Nombres de Bordeaux

For any Eichler order 𝒪 ( D , N ) of level N in an indefinite quaternion algebra of discriminant D there is a Fuchsian group Γ ( D , N ) SL ( 2 , ) and a Shimura curve X ( D , N ) . We associate to 𝒪 ( D , N ) a set ( 𝒪 ( D , N ) ) of binary quadratic forms which have semi-integer quadratic coefficients, and we develop a classification theory, with respect to Γ ( D , N ) , for primitive forms contained in ( 𝒪 ( D , N ) ) . In particular, the classification theory of primitive integral binary quadratic forms by SL ( 2 , ) is recovered. Explicit fundamental domains for Γ ( D , N ) allow the characterization...

Binomial squares in pure cubic number fields

Franz Lemmermeyer (2012)

Journal de Théorie des Nombres de Bordeaux

Let K = ( ω ) , with ω 3 = m a positive integer, be a pure cubic number field. We show that the elements α K × whose squares have the form a - ω for rational numbers a form a group isomorphic to the group of rational points on the elliptic curve E m : y 2 = x 3 - m . This result will allow us to construct unramified quadratic extensions of pure cubic number fields K .

Binomials transformation formulae for scaled Fibonacci numbers

Edyta Hetmaniok, Bożena Piątek, Roman Wituła (2017)

Open Mathematics

The aim of the paper is to present the binomial transformation formulae of Fibonacci numbers scaled by complex multipliers. Many of these new and nontrivial relations follow from the fundamental properties of the so-called delta-Fibonacci numbers defined by Wituła and Słota. The paper contains some original relations connecting the values of delta-Fibonacci numbers with the respective values of Chebyshev polynomials of the first and second kind.

Birational geometry of quadrics

Burt Totaro (2009)

Bulletin de la Société Mathématique de France

We construct new birational maps between quadrics over a field. The maps apply to several types of quadratic forms, including Pfister neighbors, neighbors of multiples of a Pfister form, and half-neighbors. One application is to determine which quadrics over a field are ruled (that is, birational to the projective line times some variety) in a larger range of dimensions. We describe ruledness completely for quadratic forms of odd dimension at most 17, even dimension at most 10, or dimension 14....

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