Group theory

Leinster group

In mathematics, a Leinster group is a finite group whose order equals the sum of the orders of its proper normal subgroups. The Leinster groups are named after Tom Leinster, a mathematician at the University of Edinburgh, who wrote about them in a paper written in 1996 but not published until 2001. He called them "perfect groups" and later "immaculate groups",but they were renamed as the Leinster groups by because "perfect group" already had a different meaning (a group that equals its commutator subgroup). Leinster groups give a group-theoretic way of analyzing the perfect numbers and of approaching the still-unsolved problem of the existence of odd perfect numbers.For a cyclic group, the orders of the subgroups are just the divisors of the order of the group,so a cyclic group is a Leinster group if and only if its order is a perfect number. More strongly, as Leinster proved, an abelian group is a Leinster group if and only if it is a cyclic group whose order is a perfect number. Moreover Leinster showed that dihedral Leinster groups are in one-to-one correspondence with odd perfect numbers, so the existence of odd perfect numbers is equivalent to the existence of dihedral Leinster groups. (Wikipedia).

Video thumbnail

GT2. Definition of Subgroup

Abstract Algebra: We define the notion of a subgroup and provide various examples. We also consider cyclic subgroups and subgroups generated by subsets in a given group G. Example include A4 and D8. U.Reddit course materials available at http://ureddit.com/class/23794/intro-to-group-

From playlist Abstract Algebra

Video thumbnail

Group Definition (expanded) - Abstract Algebra

The group is the most fundamental object you will study in abstract algebra. Groups generalize a wide variety of mathematical sets: the integers, symmetries of shapes, modular arithmetic, NxM matrices, and much more. After learning about groups in detail, you will then be ready to contin

From playlist Abstract Algebra

Video thumbnail

Symmetric Groups (Abstract Algebra)

Symmetric groups are some of the most essential types of finite groups. A symmetric group is the group of permutations on a set. The group of permutations on a set of n-elements is denoted S_n. Symmetric groups capture the history of abstract algebra, provide a wide range of examples in

From playlist Abstract Algebra

Video thumbnail

Quotient group example

Now that we know what a quotient group is, let's take a look at an example to cement our understanding of the concepts involved.

From playlist Abstract algebra

Video thumbnail

Michael Wibmer: Etale difference algebraic groups

Find this video and other talks given by worldwide mathematicians on CIRM's Audiovisual Mathematics Library: http://library.cirm-math.fr. And discover all its functionalities: - Chapter markers and keywords to watch the parts of your choice in the video - Videos enriched with abstracts, b

From playlist Algebraic and Complex Geometry

Video thumbnail

Definition of a group Lesson 24

In this video we take our first look at the definition of a group. It is basically a set of elements and the operation defined on them. If this set of elements and the operation defined on them obey the properties of closure and associativity, and if one of the elements is the identity el

From playlist Abstract algebra

Video thumbnail

CTNT 2018 - "Factoring with Elliptic Curves" by Jeremy Teitelbaum

This is lecture on "Factoring with Elliptic Curves", by Jeremy Teitelbaum, during CTNT 2018, the Connecticut Summer School in Number Theory. For more information about CTNT and other resources and notes, see https://ctnt-summer.math.uconn.edu/

From playlist CTNT 2018 - Guest Lectures

Video thumbnail

Factoring with Elliptic Curves - Jeremy Teitelbaum [2018]

May 30: Jeremy Teitelbaum (UConn) Title: Factoring with elliptic curves. Abstract: Lenstra’s elliptic curve algorithm ([1]) for factoring is a standard piece of the toolkit for computational number theory. I will give a brief introduction to this algorithm. [1] H. Lenstra, Factoring integ

From playlist Number Theory

Video thumbnail

What is a Group? | Abstract Algebra

Welcome to group theory! In today's lesson we'll be going over the definition of a group. We'll see the four group axioms in action with some examples, and some non-examples as well which violate the axioms and are thus not groups. In a fundamental way, groups are structures built from s

From playlist Abstract Algebra

Video thumbnail

15 - Algorithmic aspects of the Galois theory in recent times

Orateur(s) : M. Singer Public : Tous Date : vendredi 28 octobre Lieu : Institut Henri Poincaré

From playlist Colloque Evariste Galois

Video thumbnail

FitzGerald Dynasty Family Tree | Irish Genealogy

Book series based on the Norman invasion of Ireland: https://www.ruadhbutler.com/ Download the chart (free): https://cdn.shopify.com/s/files/1/1835/6621/files/fitzgerald.png CREDITS: Chart: Matt Baker Script/Narration: Matt Baker Editing: Jack Rackam Intro animation: Syawish Rehman Int

From playlist Royal Family Trees

Video thumbnail

301.2 Definition of a Group

A group is (in a sense) the simplest structure in which we can do the familiar tasks associated with "algebra." First, in this video, we review the definition of a group.

From playlist Modern Algebra - Chapter 15 (groups)

Video thumbnail

Heuristics for lambda Invariants - Sonal Jain

Sonal Jain New York University February 17, 2011 The λλ-invariant is an invariant of an imaginary quadratic field that measures the growth of class numbers in cyclotomic towers over the field. It also measures the number of zeroes of an associated pp-adic L-function. In this talk, I will d

From playlist Mathematics

Video thumbnail

Pär Kurlberg: Class number statistics for imaginary quadratic fields Pär Kurlberg

Abstract: The number F(h) of imaginary quadratic fields with class number h is of classical interest: Gauss' class number problem asks for a determination of those fields counted by F(h). The unconditional computation of F(h) for h x is less or equal to y 100 was completed by M. Watkins, a

From playlist Number Theory

Video thumbnail

Nina Otter (4/23/19): The magnitude of a metric space

Title: The magnitude of a metric space Abstract: The magnitude is an isometric invariant of metric spaces that was introduced by Tom Leinster in 2010, and is currently the object of intense research. Magnitude encodes many invariants of a metric space such as volume, dimension, capacity,

From playlist AATRN 2019

Video thumbnail

Abstract Algebra | The dihedral group

We present the group of symmetries of a regular n-gon, that is the dihedral group D_n. http://www.michael-penn.net http://www.randolphcollege.edu/mathematics/

From playlist Abstract Algebra

Video thumbnail

The Structure of the Group of Rational Points of an Abelian Variety (CTNT Online, June 12-14, 2020)

This video was created for the CTNT 2020 Conference (June 12-14, 2020): https://ctnt-summer.math.uconn.edu/ctnt-conference-2020-online/ (Preprint) The Structure of the Group of Rational Points of an Abelian Variety over a Finite Field: https://arxiv.org/abs/2006.00637 My contact informat

From playlist CTNT 2020 - Conference Videos

Video thumbnail

GT1. Definition of Group

Abstract Algebra: We introduce the notion of a group and describe basic properties. Examples given include familiar abelian groups and the symmetric groups. U.Reddit course materials available at http://ureddit.com/class/23794/intro-to-group-theory Master list at http://mathdoctorbob.o

From playlist Abstract Algebra

Related pages

Order (group theory) | If and only if | Group (mathematics) | Symmetric group | Mathematical proof | Alternating group | Non-abelian group | Finite group | Dihedral group | Mathematics | P-group | Divisor | Normal subgroup | Group theory | Cyclic group | Integer sequence | Perfect group | Perfect number | Prime number | Subgroup | Parity (mathematics) | Commutator subgroup | Abelian group