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The Sylow subgroups of the symmetric groups are important examples of p-groups. They are more easily described in special cases first: The Sylow p-subgroups of the symmetric group of degree p are just the cyclic subgroups generated by p-cycles. There are (p − 1)!/(p − 1) = (p − 2)! such subgroups simply by counting generators.
Subgroups of cyclic groups. In abstract algebra, every subgroup of a cyclic group is cyclic. Moreover, for a finite cyclic group of order n, every subgroup's order is a divisor of n, and there is exactly one subgroup for each divisor. [1][2] This result has been called the fundamental theorem of cyclic groups. [3][4]
In the quaternion group of order 8, each of the cyclic subgroups of order 4 is normal, but none of these are characteristic. However, the subgroup, {1, −1}, is characteristic, since it is the only subgroup of order 2. If n is even, the dihedral group of order 2n has 3 subgroups of index 2, all of which are normal. One of these is the cyclic ...
The Klein four-group is the smallest non-cyclic group. It is, however, an abelian group , and isomorphic to the dihedral group of order (cardinality) 4, symbolized D 4 {\displaystyle D_{4}} (or D 2 {\displaystyle D_{2}} , using the geometric convention); other than the group of order 2, it is the only dihedral group that is abelian.
A cyclic group is a group which is equal to one of its cyclic subgroups: G = g for some element g, called a generator of G. For a finite cyclic group G of order n we have G = {e, g, g2, ... , gn−1}, where e is the identity element and gi = gj whenever i ≡ j (mod n); in particular gn = g0 = e, and g−1 = gn−1.
The group {1, −1} above and the cyclic group of order 3 under ordinary multiplication are both examples of abelian groups, and inspection of the symmetry of their Cayley tables verifies this. In contrast, the smallest non-abelian group, the dihedral group of order 6 , does not have a symmetric Cayley table.
This follows from inspection of 5-cycles: each 5-cycle generates a group of order 5 (thus a Sylow subgroup), there are 5!/5 = 120/5 = 24 5-cycles, yielding 6 subgroups (as each subgroup also includes the identity), and S n acts transitively by conjugation on the set of cycles of a given class, hence transitively by conjugation on these subgroups.
For n = 3, 4 there are two additional one-dimensional irreducible representations, corresponding to maps to the cyclic group of order 3: A 3 ≅ C 3 and A 4 → A 4 /V ≅ C 3. For n ≥ 7 , there is just one irreducible representation of degree n − 1 , and this is the smallest degree of a non-trivial irreducible representation.