Finite linear spaces with two consecutive line degrees

Let L be a non-trivial finite linear space in which every line has n or n+1 points. We describe L completely subject to the following restrictions on n and on the number of points p: p≤n ²+n?1 and n≥3; n ²+n+2≤p≤n ²+2n?1 and n≥3; p=n ²+2n and n≥4; p=n ²+2n+2 and n≥3; p=n ²+2n+3 and n≥4.     

Fast algorithms for determining the linear complexities of sequences over GF(p m) with the period 3n

In this paper, for the the primes p such that 3 is a divisor of p ? 1, we prove a result which reduces the computation of the linear complexity of a sequence over GF(p ^m) (any positive integer m) with the period 3n (n and p ^m ? 1 are coprime) to the computation of the linear complexities of three sequences with the period n. Combined with some known algorithms such as generalized Games-Chan algorithm, Berlekamp-Massey algorithm and Xiao-Wei-Lam-Imamura algorithm, we can determine the linear complexity of any sequence over GF(p ^m) with the period 3n (n and p ^m ? 1 are coprime) more efficiently.     

Small point sets of PG(n, q 3) intersecting each k-subspace in 1 mod q points

The main result of this paper is that point sets of PG(n, q ³), q = p ^h , p ≥ 7 prime, of size less than 3(q ^3(n?k) + 1)/2 intersecting each k-space in 1 modulo q points (these are always small minimal blocking sets with respect to k-spaces) are linear blocking sets. As a consequence, we get that minimal blocking sets of PG(n, p ³), p ≥ 7 prime, of size less than 3(p ^3(n?k) + 1)/2 with respect to k-spaces are linear. We also give a classification of small linear blocking sets of PG(n, q ³) which meet every (n ? 2)-space in 1 modulo q points.     

Semisymmetric graphs of order 6p 2 and prime valency

In this paper, we investigate semisymmetric graphs of order 6p2 and of prime valency. First, we give a classification of the quasiprimitive permutation groups of degree dividing 3p2, and then, on the basis of the classification result, we prove that, for primes k and p, a connected graph Γ of order 6p2 and valency k is semisymmetric if and only if k = 3 and either Γ is the Gray graph, or p ≡ 1 (mod 6) and Γ is isomorphic to one known graph.     

Pentavalent symmetric graphs of order 2p3

A graph is symmetric or 1-regular if its automorphism group is transitive or regular on the arc set of the graph, respectively. We classify the connected pentavalent symmetric graphs of order 2p~3 for each prime p. All those symmetric graphs appear as normal Cayley graphs on some groups of order 2p~3 and their automorphism groups are determined. For p = 3, no connected pentavalent symmetric graphs of order 2p~3 exist. However, for p = 2 or 5, such symmetric graph exists uniquely in each case. For p 7, the connected pentavalent symmetric graphs of order 2p~3 are all regular covers of the dipole Dip5 with covering transposition groups of order p~3, and they consist of seven infinite families; six of them are 1-regular and exist if and only if 5 |(p- 1), while the other one is 1-transitive but not 1-regular and exists if and only if 5 |(p ± 1). In the seven infinite families, each graph is unique for a given order.     

On the representation of integers by p-adic diagonal forms

Let p be an odd prime, let d be a positive integer such that (d,p?1)=1, let r denote the p-adic valuation of d and let m=1+3+3²+…+3^r. It is shown that for every p-adic integer n the equation Σ_i=1^mX_i^d=n has a nontrivial p-adic solution. It is also shown that for all p-adic units a₁, a₂, a₃, a₄ and all p-adic integers n the equation Σ_i=1⁴a_iX_i^p=n has a nontrivial p-adic solution. A corollary to each of these results is that every p-adic integer is a sum of four pth powers of p-adic integers.     

Best constants in Sobolev inequalities for compact manifolds of nonpositive curvature

Let (M,g) be a smooth compact Riemannian n-manifold, n ≥ 2, let p(1, n) real, and let H₁^p (M) be the standard Sobolev space of order p. By the Sobolev embedding theorem, H₁^p(M) ⊂ L^p* (M) where p^* = np/(n - p). Classically, this leads to some Sobolev inequality (I_p¹), and then to some Sobolev inequality (I_p^p) where each term in (I_p¹) is elevated to the power p. Long standing questions were to know if the optimal versions with respect to the first constant of (I_p¹) and (I_p^p) do hold. Such questions received an affirmative answer by Hebey-Vaugon for p = 2, and on what concerns (I_p¹), by Aubin for two-dimensional manifolds and for manifolds of constant sectional curvature. Recently, Druet proved that for p > 2, and p² < n, the optimal version of (I_p^p) is false if the scalar curvature of g is positive somewhere, while for p > 1, the optimal version of (I_p^p) does hold on flat torii and compact hyperbolic spaces. We prove here that the optimal version of (I_p^p), p > 1, does hold for compact manifolds of nonpositive sectional curvature in any dimension where the Cartan-Hadamard conjecture is true. In particular, since the Cartan-Hadmard conjecture is true in dimensions 2, 3, and 4, the optimal version of (I_p^p) does hold on any compact manifold of nonpositive sectional curvature of dimension 2, 3, or 4.     

Small point sets of PG(n, p 3h ) intersecting each line in 1 mod p h points

The main result of this paper is that point sets of PG(n, q), q = p ^3h , p ≥ 7 prime, of size < 3(q ^n-1 + 1)/2 intersecting each line in 1 modulo ${\sqrt[3] q}$ points (these are always small minimal blocking sets with respect to lines) are linear blocking sets. As a consequence, we get that minimal blocking sets of PG(n, p ³), p ≥ 7 prime, of size < 3(p ^3(n-1) + 1)/2 with respect to lines are always linear.     

Divisibility of fermat quotients

For any ? > 0 and all primes p, with the exception of primes from a set with relative zero density, there exists a natural number a ≤ (log p)^3/2+? for which the congruence a ^p?1 ≡ 1 (modp ²) does not hold.     

The diophantine equation x3 − 3xy2 − y3 = 1 and related equations

The diophantine equation of the title has been solved by Ljunggren, by indirect use of the p-adic method (use is made of intermediate algebraic extensions). It is generally accepted that an immediate application of the p-adic method for the aforementioned equation is impossible. In this paper, however, this view was overthrown by first solving x² + 3 = 4y³ and then x³ ? 3xy² ? y³ = 1 with direct application of the p-adic method, avoiding the use of intermediate algebraic extensions, fulfilling thus a desire of Professor Mordell. The method used in this paper has a general character, as it is shown in Appendix B, where three more examples are given.     

Solvability of cubic equations in p-ADIC integers (p > 3)

We give a criterion for the existence of solutions to an equation of the form x ³ + ax = b, where a, b ∈ ? _p , in p-adic integers for p > 3. Moreover, in the case when the equation x ³ + ax = b is solvable, we give necessary and sufficient recurrent conditions on a p-adic number x ∈ ?* _p under which x is a solution to the equation.     

Finite presentation of alternating groups

Graham Higman posed the question: How small can the integersp andq be made, while maintaining the property that all but finitly many alternating and symmetric groups are factor groups of Δ(2,p,q)=<x,y:x ²=y ^p =3 (xy) ^q =1>? He proved that for a sufficiently largen, the alternating group is a homomorphic image of the triangle group Δ(2,p,q) wherep=3 andq=7. Later, his result was generalized by proving the result forp=3 andq≥7. Choosingp=4 andq≥17 in this paper we have answered the “Hiqman Question”.     

Cubic edge-transitive graphs of order 2p3

Let p be a prime. It was shown by Folkman (J. Combin. Theory 3 (1967) 215) that a regular edge-transitive graph of order 2p or 2p² is necessarily vertex-transitive. In this paper an extension of his result in the case of cubic graphs is given. It is proved that, with the exception of the Gray graph on 54 vertices, every cubic edge-transitive graph of order 2p³ is vertex-transitive.     

The cubic Fermat equation and complex multiplication on the Deuring normal form

The arithmetic on elliptic curves in Deuring normal form is shown to be related to solutions of the Fermat equation 27X ³+27Y ³=X ³ Y ³. This arithmetic is used to give conditions for the existence of multipliers μ on supersingular elliptic curves in characteristic p for which μ ²=?3p. Together with an explicit factorization of a certain class equation, these conditions imply that the number of irreducible binomial quadratic factors (mod p) of the Legendre polynomial P _(p?e)/3(x) of degree (p?e)/3 is a simple linear function of the class number of the quadratic field \(\mathbb{Q}(\sqrt{-3p})\).     

The diophantine equation x 2 + 2 a · 17 b = y n

Let ?, ? be the sets of all integers and positive integers, respectively. Let p be a fixed odd prime. Recently, there have been many papers concerned with solutions (x, y, n, a, b) of the equation x ² + 2 ^a p ^b = y ⁿ , x, y, n ε ?, gcd(x, y) = 1, n ? 3, a, b ε ?, a ? 0, b ? 0. And all solutions of it have been determined for the cases p = 3, p = 5, p = 11 and p = 13. In this paper, we mainly concentrate on the case p = 3, and using certain recent results on exponential diophantine equations including the famous Catalan equation, all solutions (x, y, n, a, b) of the equation x ²+2 ^a · 17 ^b = y ⁿ , x, y, n ε ?, gcd(x, y) = 1, n ? 3, a, b ∈ ?, a ? 0, b ? 0, are determined.     

Hasse invariants and anomalous primes for elliptic curves with complex multiplication

Let C be an elliptic curve defined over Q. Let p be a prime where C has good reduction. By definition, p is anomalous for C if the Hasse invariant at p is congruent to 1 modulo p. The phenomenon of anomalous primes has been shown by Mazur to be of great interest in the study of rational points in towers of number fields. This paper is devoted to discussing the Hasse invariants and the anomalous primes of elliptic curves admitting complex multiplication. The two special cases Y² = X³ + a₄X and Y² = X³ + a₆ are studied at considerable length. As corollaries, some results in elementary number theory concerning the residue classes of the binomial coefficients (_n²ⁿ) (Resp. (_n³ⁿ)) modulo a prime p = 4n + 1 (resp. p = 6n + 1) are obtained. It is shown that certain classes of elliptic curves admitting complex multiplication do not have any anomalous primes and that others admit only very few anomalous primes.     

The Estermann cubic problem with almost equal summands

We prove an asymptotic formula for the number of representations of a sufficiently large natural number N as the sum of two primes p ₁ and p ₂ and the cube of a natural numbermsatisfying the conditions |p _i ? N/3| ≤ H, |m ³ ? N/3| ≤ H, H ≥ N ^5/6 ? ¹⁰.     

A series of Siamese twin designs

A {0,±1}-matrix S is called a Siamese twin design sharing the entries of I if S=I+K−L, where I,K,L are nonzero {0,1}-matrices and both I+K and I+L are incidence matrices of symmetric designs with the same parameters. Let p and 2p+3 be prime powers and . We construct a Siamese twin design with parameters (4(p+1)²,2p²+3p+1,p²+p).     

Adams theorem on Bernoulli numbers revisited

If we denote B_n to be nth Bernoulli number, then the classical result of Adams (J. Reine Angew. Math. 85 (1878) 269) says that p^?|n and (p−1)?n, then p^?|B_n where p is any odd prime p>3. We conjecture that if (p−1)?n, p^?|n and p?+1?n for any odd prime p>3, then the exact power of p dividing B_n is either ? or ?+1. The main purpose of this article is to prove that this conjecture is equivalent to two other unproven hypotheses involving Bernoulli numbers and to provide a positive answer to this conjecture for infinitely many n.