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G = D9  order 18 = 2·32

Dihedral group

metacyclic, supersoluble, monomial, Z-group, 2-hyperelementary

Aliases: D9, C9⋊C2, C3.S3, sometimes denoted D18 or Dih9 or Dih18, SmallGroup(18,1)

Series: Derived ►Chief ►Lower central ►Upper central

C1 — C9 — D9
C1 — C3 — C9 — D9
C9 — D9
C1

Generators and relations for D9
 G = < a,b | a9=b2=1, bab=a-1 >

9C2
3S3

Character table of D9

 class 1239A9B9C
 size 192222
ρ1111111    trivial
ρ21-11111    linear of order 2
ρ3202-1-1-1    orthogonal lifted from S3
ρ420-1ζ95+ζ94ζ97+ζ92ζ98+ζ9    orthogonal faithful
ρ520-1ζ98+ζ9ζ95+ζ94ζ97+ζ92    orthogonal faithful
ρ620-1ζ97+ζ92ζ98+ζ9ζ95+ζ94    orthogonal faithful

Permutation representations of D9
►On 9 points - transitive group 9T3
Generators in S9
(1 2 3 4 5 6 7 8 9)
(1 9)(2 8)(3 7)(4 6)
 
G:=sub<Sym(9)| (1,2,3,4,5,6,7,8,9), (1,9)(2,8)(3,7)(4,6)>;
 
G:=Group( (1,2,3,4,5,6,7,8,9), (1,9)(2,8)(3,7)(4,6) );
 
G=PermutationGroup([[(1,2,3,4,5,6,7,8,9)], [(1,9),(2,8),(3,7),(4,6)]])
 
G:=TransitiveGroup(9,3);
 

►Regular action on 18 points - transitive group 18T5
Generators in S18
(1 2 3 4 5 6 7 8 9)(10 11 12 13 14 15 16 17 18)
(1 13)(2 12)(3 11)(4 10)(5 18)(6 17)(7 16)(8 15)(9 14)
 
G:=sub<Sym(18)| (1,2,3,4,5,6,7,8,9)(10,11,12,13,14,15,16,17,18), (1,13)(2,12)(3,11)(4,10)(5,18)(6,17)(7,16)(8,15)(9,14)>;
 
G:=Group( (1,2,3,4,5,6,7,8,9)(10,11,12,13,14,15,16,17,18), (1,13)(2,12)(3,11)(4,10)(5,18)(6,17)(7,16)(8,15)(9,14) );
 
G=PermutationGroup([[(1,2,3,4,5,6,7,8,9),(10,11,12,13,14,15,16,17,18)], [(1,13),(2,12),(3,11),(4,10),(5,18),(6,17),(7,16),(8,15),(9,14)]])
 
G:=TransitiveGroup(18,5);
 

D9 is a maximal subgroup of
 C9⋊C6  C9⋊S3  C3.S4  C52⋊D9
 D9p: D27  D45  D63  D99  D117  D153  D171  D207 ...
D9 is a maximal quotient of
 C9⋊S3  C3.S4  C52⋊D9
 C3p.S3: Dic9  D27  D45  D63  D99  D117  D153  D171 ...

Polynomial with Galois group D9 over ℚ
actionf(x)Disc(f)
9T3x9+3x8-67x7-226x6+699x5+1211x4-3137x3+940x2+904x-392222·74·132·196·292·2294·5472

Matrix representation of D9 ►in GL2(𝔽17) generated by

1610
714
,
146
103
G:=sub<GL(2,GF(17))| [16,7,10,14],[14,10,6,3] >;
 

D9 in GAP, Magma, Sage, TeX

D_9
 
% in TeX
 
G:=Group("D9");
 
// GroupNames label
 
G:=SmallGroup(18,1);
 
// by ID
 
G=gap.SmallGroup(18,1);
 
# by ID
 
G:=PCGroup([3,-2,-3,-3,97,22,110]);
 
// Polycyclic
 
G:=Group<a,b|a^9=b^2=1,b*a*b=a^-1>;
 
// generators/relations
 

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Subgroup lattice of D9 in TeX
Character table of D9 in TeX

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