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Landau’s function for one million billions

Marc Deléglise, Jean-Louis Nicolas, Paul Zimmermann (2008)

Journal de Théorie des Nombres de Bordeaux

Let 𝔖 n denote the symmetric group with n letters, and g ( n ) the maximal order of an element of 𝔖 n . If the standard factorization of M into primes is M = q 1 α 1 q 2 α 2 ... q k α k , we define ( M ) to be q 1 α 1 + q 2 α 2 + ... + q k α k ; one century ago, E. Landau proved that g ( n ) = max ( M ) n M and that, when n goes to infinity, log g ( n ) n log ( n ) .There exists a basic algorithm to compute g ( n ) for 1 n N ; its running time is 𝒪 N 3 / 2 / log N and the needed memory is 𝒪 ( N ) ; it allows computing g ( n ) up to, say, one million. We describe an algorithm to calculate g ( n ) for n up to 10 15 . The main idea is to use the so-called -superchampion...

Large free subgroups of automorphism groups of ultrahomogeneous spaces

Szymon Głąb, Filip Strobin (2015)

Colloquium Mathematicae

We consider the following notion of largeness for subgroups of S . A group G is large if it contains a free subgroup on generators. We give a necessary condition for a countable structure A to have a large group Aut(A) of automorphisms. It turns out that any countable free subgroup of S can be extended to a large free subgroup of S , and, under Martin’s Axiom, any free subgroup of S of cardinality less than can also be extended to a large free subgroup of S . Finally, if Gₙ are countable groups, then...

Le diagramme du treillis permutoèdre est intersection des diagrammes de deux produits directs d'ordres totaux

Claude Le Conte de Poly-Barbut (1990)

Mathématiques et Sciences Humaines

Deux codages sont utilisés sur l’ensemble des permutations ou ordres totaux sur un ensemble fini à n éléments et à chacun de ces codages est associé un produit direct d’ordres totaux. On démontre que le diagramme du treillis permutoèdre (ou ordre de Bruhat faible sur le groupe symétrique S n ) est intersection des diagrammes des deux produits directs de n - 1 ordres totaux à 2 , 3 , . . . , n éléments.

Malnormal subgroups and Frobenius groups: basics and examples

Pierre de la Harpe, Claude Weber (2014)

Confluentes Mathematici

Malnormal subgroups occur in various contexts. We review a large number of examples, and compare the general situation to that of finite Frobenius groups of permutations.In a companion paper [18], we analyse when peripheral subgroups of knot groups and 3 -manifold groups are malnormal.

Maximal clones and maximal permutation groups

Péter P. Pálfy (2007)

Discussiones Mathematicae - General Algebra and Applications

A fundamental result in universal algebra is the theorem of Rosenberg describing the maximal subclones in the clone of all operations over a finite set. In group theory, the maximal subgroups of the symmetric groups are classified by the O'Nan-Scott Theorem. We shall explore the similarities and differences between these two analogous major results. In addition, we show that a primitive permutation group of diagonal type can be maximal in the symmetric group only if its socle is the direct product...

Multiples of left loops and vertex-transitive graphs

Eric Mwambene (2005)

Open Mathematics

Via representation of vertex-transitive graphs on groupoids, we show that left loops with units are factors of groups, i.e., left loops are transversals of left cosets on which it is possible to define a binary operation which allows left cancellation.

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