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Abstract: This paper is about the pole of some Eisenstein series for classical groups over a number field. In a previous paper, we have shown how to normalize intertwining operators in such a way that they are holomorphic for positive parameters. Here we show that the image of such operators is (in the interesting cases) either 0 or an irreducible representation. This enables us to compute explicitly the residue of the Eisenstein series obtained from square integrable cohomological representations. At the end of the paper we give necessary and sufficient conditions in terms of Arthurʼs data in order that a square integrable cohomological representation is cuspidal; the conditions are not totally satisfactory and we explain what we expect when Arthurʼs results will be fully available. [Copyright &y& Elsevier]

Let N be the set of positive integers and A a subset of N. For n∈N, let p(A,n) denote the number of partitions of n with parts in A. In the paper J. Number Theory 73 (1998) 292, Nicolas et al. proved that, given any N∈N and B⊂{1,2,…,N}, there is a unique set A=A0(B,N), such that p(A,n) is even for n>N. Soon after, Ben Saı¨d and Nicolas (Acta Arith. 106 (2003) 183) considered σ(A,n)=∑d∣n,d∈Ad, and proved that for all k≥0, the sequence (σ(A,2kn) mod 2k+1)n≥1 is periodic on n. In this paper, we generalise the above works for any formal power series f in F2[z] with f(0)=1, by constructing a set A such that the generating function fA of A is congruent to f modulo 2, and by showing that if f=P/Q, where P and Q are in F2[z] with P(0)=Q(0)=1, then for all k≥0 the sequence (σ(A,2kn) mod 2k+1)n≥1 is periodic on n. [Copyright &y& Elsevier]

Abstract: The K-theory of a functor may be viewed as a relative version of the K-theory of a ring. After its description, we prove a Mayer–Vietoris exact sequence in this framework. In the case of a Galois extension of a number field with rings of integers A, B respectively, this K-theory of the “norm functor” is an extension of a subgroup of the ideal class group of F by the Tate cohomology group . The Mayer–Vietoris exact sequence enables us to describe in a quite explicit way a quotient of the subgroup of the ideal class group , where N is the norm. We also prove a short exact sequence where is the group of semi-local units of F. Finally, we conclude this paper by applications of our methods to Number Theory. [Copyright &y& Elsevier]

Abstract: Let p be an odd prime and , where m is a positive integer. Let be a qth primitive root of 1 and be the ring of integers in . In [I. Gaál, L. Robertson, Power integral bases in prime-power cyclotomic fields, J. Number Theory 120 (2006) 372–384] I. Gaál and L. Robertson show that if , where is the class number of , then if is a generator of (in other words ) either α is equals to a conjugate of an integer translate of or is an odd integer. In this paper we show that we can remove the hypothesis over . In other words we show that if is a generator of then either α is a conjugate of an integer translate of or is an odd integer. [Copyright &y& Elsevier]

Abstract: In this paper, we are interested in diophantine equations of type where F is a separable homogeneous form of degree ⩾3 with integer coefficients, d a fixed integer ⩾1 and p a prime number ⩾7. As a consequence of the abc conjecture, if p is sufficiently large and is a nontrivial proper solution of the above equation, we have . In the case where F has degree 3, we associate to an elliptic curve defined over called the Frey curve or Hellegouarch–Frey curve. This allows us to deduce our conjecture from another one about elliptic curves attributed to G. Frey and B. Mazur (which is itself a consequence of the abc conjecture). We then applied our construction to the study of an explicit form. We give some results about the set of nontrivial proper solutions of the equation considered for several values of d. [Copyright &y& Elsevier]