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On some subgroup chains related to Kneser’s theorem

Yahya Ould Hamidoune, Oriol Serra, Gilles Zémor (2008)

Journal de Théorie des Nombres de Bordeaux

A recent result of Balandraud shows that for every subset S of an abelian group G there exists a non trivial subgroup H such that | T S | | T | + | S | - 2 holds only if H S t a b ( T S ) . Notice that Kneser’s Theorem only gives { 1 } S t a b ( T S ) .This strong form of Kneser’s theorem follows from some nice properties of a certain poset investigated by Balandraud. We consider an analogous poset for nonabelian groups and, by using classical tools from Additive Number Theory, extend some of the above results. In particular we obtain short proofs of Balandraud’s...

On some subgroups of the multiplicative group of finite rings

José Felipe Voloch (2004)

Journal de Théorie des Nombres de Bordeaux

Let S be a subset of F q , the field of q elements and h F q [ x ] a polynomial of degree d > 1 with no roots in S . Consider the group generated by the image of { x - s s S } in the group of units of the ring F q [ x ] / ( h ) . In this paper we present a number of lower bounds for the size of this group. Our main motivation is an application to the recent polynomial time primality testing algorithm [AKS]. The bounds have also applications to graph theory and to the bounding of the number of rational points on abelian covers of the projective...

On some universal sums of generalized polygonal numbers

Fan Ge, Zhi-Wei Sun (2016)

Colloquium Mathematicae

For m = 3,4,... those pₘ(x) = (m-2)x(x-1)/2 + x with x ∈ ℤ are called generalized m-gonal numbers. Sun (2015) studied for what values of positive integers a,b,c the sum ap₅ + bp₅ + cp₅ is universal over ℤ (i.e., any n ∈ ℕ = 0,1,2,... has the form ap₅(x) + bp₅(y) + cp₅(z) with x,y,z ∈ ℤ). We prove that p₅ + bp₅ + 3p₅ (b = 1,2,3,4,9) and p₅ + 2p₅ + 6p₅ are universal over ℤ, as conjectured by Sun. Sun also conjectured that any n ∈ ℕ can be written as p ( x ) + p ( y ) + p 11 ( z ) and 3p₃(x) + p₅(y) + p₇(z) with x,y,z ∈ ℕ; in...

On special values of theta functions of genus two

Ehud De Shalit, Eyal Z. Goren (1997)

Annales de l'institut Fourier

We study a certain finitely generated multiplicative subgroup of the Hilbert class field of a quartic CM field. It consists of special values of certain theta functions of genus 2 and is analogous to the group of Siegel units. Questions of integrality of these specials values are related to the arithmetic of the Siegel moduli space.

On square classes in generalized Fibonacci sequences

Zafer Şiar, Refik Keskin (2016)

Acta Arithmetica

Let P and Q be nonzero integers. The generalized Fibonacci and Lucas sequences are defined respectively as follows: U₀ = 0, U₁ = 1, V₀ = 2, V₁ = P and U n + 1 = P U + Q U n - 1 , V n + 1 = P V + Q V n - 1 for n ≥ 1. In this paper, when w ∈ 1,2,3,6, for all odd relatively prime values of P and Q such that P ≥ 1 and P² + 4Q > 0, we determine all n and m satisfying the equation Uₙ = wUₘx². In particular, when k|P and k > 1, we solve the equations Uₙ = kx² and Uₙ = 2kx². As a result, we determine all n such that Uₙ = 6x².

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