Symmetric group:S3

Definition

Verbal definitions

The symmetric group $S_{3}$ can be defined in the following equivalent ways:

• It is the symmetric group on a set of three elements, viz., the group of all permutations of a three-element set. In particular, it is a symmetric group of prime degree and symmetric group of prime power degree.
• It is the dihedral group of order six (degree three), viz., the group of (not necessarily orientation-preserving) symmetries of the equilateral triangle.

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• It is the special linear group of degree two $SL(2,2)$ over the field of two elements. It turns out that, because of the nature of the prime two, it is also the projective special linear group of degree two $PSL(2,2)$, the general linear group of degree two $GL(2,2)$, and the projective general linear group of degree two $PGL(2,2)$.
• It is the general affine group of degree $1$ over the field of three elements, i.e., $GA(1,3)$ (sometimes also written as $AGL(1,3)$).
• It is the von Dyck group with parameters $(3,2,2)$, and in particular, is a Coxeter group. In particular, it has the presentation:

$\langle a,b,c\mid a^{3}=b^{2}=c^{2}=abc=e\rangle$.

In the Coxeter language, this is written as:

$\langle s_{1},s_{2}\mid s_{1}^{2}=s_{2}^{2}=(s_{1}s_{2})^{3}=e\rangle$.

Multiplication table

We portray elements as permutations on the set $\{1,2,3\}$ using the cycle decomposition. The row element is multiplied on the left and the column element on the right, with the assumption of functions written on the left. This means that the column element is applied first and the row element is applied next.

Element	$()$	$(1,2)$	$(2,3)$	$(1,3)$	$(1,2,3)$	$(1,3,2)$
$()$	$()$	$(1,2)$	$(2,3)$	$(1,3)$	$(1,2,3)$	$(1,3,2)$
$(1,2)$	$(1,2)$	$()$	$(1,2,3)$	$(1,3,2)$	$(2,3)$	$(1,3)$
$(2,3)$	$(2,3)$	$(1,3,2)$	$()$	$(1,2,3)$	$(1,3)$	$(1,2)$
$(1,3)$	$(1,3)$	$(1,2,3)$	$(1,3,2)$	$()$	$(1,2)$	$(2,3)$
$(1,2,3)$	$(1,2,3)$	$(1,3)$	$(1,2)$	$(2,3)$	$(1,3,2)$	$()$
$(1,3,2)$	$(1,3,2)$	$(2,3)$	$(1,3)$	$(1,2)$	$()$	$(1,2,3)$

If we used the opposite convention (i.e., functions written on the right), the row element is to be multiplied on the right and the column element on the left.

Here is the multiplication table where we use the one-line notation for permutations, where, as in the previous multiplication table, the column permutation is applied first and then the row permutation. Thus, with the left action convention, the row element is multiplied on the left and the column element on the right:

Element	123	213	132	321	231	312
123	123	213	132	321	231	312
213	213	123	231	312	132	321
132	132	312	123	231	321	213
321	321	231	312	123	213	132
231	231	321	213	132	312	123
312	312	132	321	213	123	231

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Families

The symmetric group on three elements is part of some important families:

Generic name for family member	Definition	Parametrization of family	Parameter value(s) for this member	Other members	Comments
symmetric group on finite set	group of all permutations on a finite set	by a nonnegative integer, denoting size of set acted on	3	click here for a list
Coxeter group	has a presentation of a particular form	Coxeter matrix describing the presentation		click here for a list	symmetric groups on finite sets are Coxeter groups
dihedral group	semidirect product of a cyclic group and a two-element group acting via the inverse map	by a positive integer that's half the order	3	click here for a list
general linear group	general linear group of finite degree over a finite field	name of field, degree	field:F2 (size two), degree two	click here for a list
projective general linear group	projective general linear group of finite degree over a finite field	name of field, degree	field:F2 (size two), degree two	click here for a list
special linear group	special linear group of finite degree over a finite field	name of field, degree	field:F2 (size two), degree two	click here for a list
projective special linear group	projective special linear group of finite degree over a finite field	name of field, degree	field:F2 (size two), degree two	click here for a list

Elements

Further information: Element structure of symmetric group:S3

Conjugacy class structure

As for any symmetric group, cycle type determines conjugacy class. The cycle types, in turn, are parametrized by the unordered integer partitions of $3$. The conjugacy classes are described below.

Partition	Partition in grouped form	Verbal description of cycle type	Elements with the cycle type in cycle decomposition notation	Elements with the cycle type in one-line notation	Size of conjugacy class	Formula for size	Even or odd? If even, splits? If splits, real in alternating group?	Element order	Formula calculating element order
1 + 1 + 1	1 (3 times)	three fixed points	$()$ -- the identity element	123	1	$\!{\frac {3!}{(1)^{3}(3!)}}$	even; no	1	$\operatorname {lcm} \{1,1,1\}$
2 + 1	2 (1 time), 1 (1 time)	transposition in symmetric group:S3: one 2-cycle, one fixed point	$(1,2)$, $(1,3)$, $(2,3)$	213, 321, 132	3	$\!{\frac {3!}{(2)(1)}}$	odd	2	$\operatorname {lcm} \{2,1\}$
3	3 (1 time)	3-cycle in symmetric group:S3: one 3-cycle	$(1,2,3)$, $(1,3,2)$	231, 312	2	$\!{\frac {3!}{3}}$	even; yes; no	3	$\operatorname {lcm} \{3\}$
Total (3 rows -- 3 being the number of unordered integer partitions of 3)	--	--	--	--	6 (equals 3!, the size of the symmetric group)	--	odd: 3 even;no: 1 even; yes; no: 2	order 1: 1, order 2: 3, order 3: 2	--

This group is one of three finite groups with the property that any two elements of the same order are conjugate. The other two are the cyclic group of order two and the trivial group.

Automorphism class structure

The classification of elements upto automorphism is the same as that upto conjugation; this is because the symmetric group on three elements is a complete group: a centerless group where every automorphism is inner.

Arithmetic functions

Basic arithmetic functions

Function	Value	Similar groups	Explanation
order (number of elements, equivalently, cardinality or size of underlying set)	6	groups with same order	As symmetric group $\!S_{k},k=3:$, $\!k!=3!=3\cdot 2\cdot 1=6$ as general linear group of degree two $\!GL(2,q),q=2:$ $\!(q^{2}-1)(q^{2}-q)=(2^{2}-1)(2^{2}-2)=6$
exponent of a group	6	groups with same order and exponent of a group | groups with same exponent of a group	Elements of order $2$ and $3$.
derived length	2	groups with same order and derived length | groups with same derived length	Cyclic subgroup of order three is abelian, has abelian quotient.
minimum size of generating set	2	groups with same order and minimum size of generating set | groups with same minimum size of generating set	$(1,2),(1,2,3)$
subgroup rank of a group	2	groups with same order and subgroup rank of a group | groups with same subgroup rank of a group	All proper subgroups are cyclic.
max-length of a group	2	groups with same order and max-length of a group | groups with same max-length of a group]	Subgroup series going through subgroup of order two or three.

Arithmetic functions of an element-counting nature

Function	Value	Similar groups	Explanation
number of conjugacy classes	3	groups with same order and number of conjugacy classes | groups with same number of conjugacy classes	The three classes are the identity element, the transpositions, and the 3-cycles.
number of equivalence classes under real conjugacy	3	groups with same order and number of equivalence classes under real conjugacy | groups with same number of equivalence classes under real conjugacy	Same as the number of conjugacy classes, because the group is an ambivalent group.
number of conjugacy classes of real elements	3	groups with same order and number of conjugacy classes of real elements | groups with same number of conjugacy classes of real elements	Same as the number of conjugacy classes, because the group is an ambivalent group.
number of equivalence classes under rational conjugacy	3	groups with same order and number of equivalence classes under rational conjugacy | groups with same number of equivalence classes under rational conjugacy	Same as the number of conjugacy classes, because the group is a rational group.
number of conjugacy classes of rational elements	3	groups with same order and number of conjugacy classes of rational elements | groups with same number of conjugacy classes of rational elements	Same as the number of conjugacy classes, because the group is an ambivalent group.

Arithmetic functions of a subgroup-counting nature

Function	Value	Similar groups	Explanation
number of subgroups	6		See subgroup structure of symmetric group:S3
number of conjugacy classes of subgroups	4
number of normal subgroups	3	groups with same order and number of normal subgroups | groups with same number of normal subgroups
number of automorphism classes of subgroups	4

Lists of numerical invariants

List	Value	Explanation/comment
conjugacy class sizes	$1,2,3$	See cycle type determines conjugacy class, element structure of symmetric group:S3, element structure of symmetric groups
order statistics	$1\mapsto 1,2\mapsto 3,3\mapsto 2$
degrees of irreducible representations	$1,1,2$	See linear representation theory of symmetric group:S3, linear representation theory of symmetric groups
orders of subgroups	$1,2,2,2,3,6$	See subgroup structure of symmetric group:S3

Group properties

Important properties

Property	Satisfied?	Explanation	Comment
Abelian group	No	$(1,2)$ and $(2,3)$ don't commute	Smallest non-abelian group
Nilpotent group	No	Centerless: The center is trivial	Smallest non-nilpotent group
Metacyclic group	Yes	Cyclic normal subgroup of order three, cyclic quotient of order two
Supersolvable group	Yes	Metacyclic implies supersolvable
Solvable group	Yes	Metacyclic implies solvable

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Other properties

Property	Satisfied?	Explanation	Comment
T-group	Yes
Monolithic group	Yes	Unique minimal normal subgroup of order three
One-headed group	Yes	Unique maximal normal subgroup of order three
Jordan-unique group	Yes	There is a unique composition series
SC-group	Yes	Every subgroup of it is a C-group	C-group means that every subgroup is permutably complemented
Rational-representation group	Yes	Symmetric groups are rational-representation
Rational group	Yes	Symmetric groups are rational	Also see classification of rational dihedral groups
Ambivalent group	Yes	Symmetric groups are ambivalent
Complete group	Yes	Symmetric groups are complete, except degrees $2,6$
Frobenius group	Yes	Frobenius kernel is alternating group, complement is any subgroup of order two.	Frobenius group on account of being $GA(1,3)$.
Camina group	Yes

Subgroups

Further information: Subgroup structure of symmetric group:S3

Quick summary

Item	Value
Number of subgroups	6 Compared with $S_{n},n=1,2,3,4,5,\dots$: 1,2,6,30,156,1455,11300, 151221
Number of conjugacy classes of subgroups	4 Compared with $S_{n},n=1,2,3,4,5,\dots$: 1,2,4,11,19,56,96,296,554,1593
Number of automorphism classes of subgroups	4 Compared with $S_{n},n=1,2,3,4,5,\dots$: 1,2,4,11,19,37,96,296,554,1593
Isomorphism classes of Sylow subgroups and the corresponding Sylow numbers and fusion systems	2-Sylow: cyclic group:Z2, Sylow number is 3, fusion system is the trivial one 3-Sylow: cyclic group:Z3, Sylow number is 1, fusion system is non-inner fusion system for cyclic group:Z3
Hall subgroups	Given that the order has only two distinct prime factors, the Hall subgroups are the whole group, trivial subgroup, and Sylow subgroups. Interestingly, all subgroups are Hall subgroups, because the order is a square-free number
maximal subgroups	maximal subgroups have order 2 (S2 in S3) and 3 (A3 in S3).
normal subgroups	There are three normal subgroups: the trivial subgroup, the whole group, and A3 in S3.

Table classifying subgroups up to automorphisms

For more information on each automorphism type, follow the link.

Automorphism class of subgroups	List of all subgroups	Isomorphism class	Order of subgroups	Index of subgroups	Number of conjugacy classes (=1 iff automorph-conjugate subgroup)	Size of each conjugacy class (=1 iff normal subgroup)	Total number of subgroups (=1 iff characteristic subgroup)	Isomorphism class of quotient (if exists)	Note
trivial subgroup	$\{()\}$	trivial group	1	6	1	1	1	symmetric group:S3	trivial
S2 in S3	$\{(),(1,2)\},\{(),(2,3)\},\{(),(1,3)\}$	cyclic group:Z2	2	3	1	3	3	--	2-Sylow
A3 in S3	$\{(),(1,2,3),(1,3,2)\}$	cyclic group:Z3	3	2	1	1	1	cyclic group:Z2	3-Sylow
whole group	$\{(),(1,2,3),(1,3,2),$ $(1,2),(1,3),(2,3)\}$	symmetric group:S3	6	1	1	1	1	trivial group
Total (4 rows)	--	--	--	--	4	--	6	--	--

Subgroup-defining functions and associated quotient-defining functions

Subgroup-defining function	What it means	Value as subgroup	Value as group	Order	Associated quotient-defining function	Value as group	Order (= index of subgroup)
center	elements that commute with every group element	trivial subgroup	trivial group	1	inner automorphism group	symmetric group:S3	6
derived subgroup	subgroup generated by all commutators	A3 in S3: $\{(),(1,2,3),(1,3,2)\}$	cyclic group:Z3	3	abelianization	cyclic group:Z2	2
Frattini subgroup	intersection of all maximal subgroups	trivial subgroup	trivial group	1	Frattini quotient	symmetric group:S3	6
Jacobson radical	intersection of all maximal normal subgroups	A3 in S3: $\{(),(1,2,3),(1,3,2)\}$	cyclic group:Z3	3	?	cyclic group:Z2	2
socle	join of all minimal normal subgroups	A3 in S3: $\{(),(1,2,3),(1,3,2)\}$	cyclic group:Z3	3	?	cyclic group:Z2	2
Fitting subgroup	join of all nilpotent normal subgroups	A3 in S3: $\{(),(1,2,3),(1,3,2)\}$	cyclic group:Z3	3	?	cyclic group:Z2	2
solvable radical	join of all solvable normal subgroups	whole group	symmetric group:S3	6	?	trivial group	1
Brauer core	largest odd-order normal subgroup	A3 in S3: $\{(),(1,2,3),(1,3,2)\}$	cyclic group:Z3	3	?	cyclic group:Z2	2
3-Sylow core or 3-core	normal core of any 3-Sylow subgroup	A3 in S3: $\{(),(1,2,3),(1,3,2)\}$	cyclic group:Z3	3	?	cyclic group:Z2	2
3-Sylow closure	normal closure of any 3-Sylow subgroup	A3 in S3: $\{(),(1,2,3),(1,3,2)\}$	cyclic group:Z3	3	?	cyclic group:Z2	2

Distinguishing features

Smallest of its kind

• This is the unique non-abelian group of smallest order. All groups of order up to $5$, and all other groups of order $6$, are abelian.
• This is the unique non-nilpotent group of smallest order. All groups of order up to $5$, and all other groups of order $6$, are nilpotent.
• This is the unique smallest nontrivial complete group.

GAP implementation

Group ID

This finite group has order 6 and has ID 1 among the groups of order 6 in GAP's SmallGroup library. For context, there are groups of order 6. It can thus be defined using GAP's SmallGroup function as:

SmallGroup(6,1)

For instance, we can use the following assignment in GAP to create the group and name it $G$:

gap> G := SmallGroup(6,1);

Conversely, to check whether a given group $G$ is in fact the group we want, we can use GAP's IdGroup function:

IdGroup(G) = [6,1]

or just do:

IdGroup(G)

to have GAP output the group ID, that we can then compare to what we want.

Other descriptions

Description	Functions used
SymmetricGroup(3)	SymmetricGroup
DihedralGroup(6)	DihedralGroup
GL(2,2)	GL