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The lattice of subgroups of the infinite cyclic group can be described in the same way, as the dual of the divisibility lattice of all positive integers. If the infinite cyclic group is represented as the additive group on the integers, then the subgroup generated by d is a subgroup of the subgroup generated by e if and only if e is a divisor ...
A metacyclic group is a group containing a cyclic normal subgroup whose quotient is also cyclic. [23] These groups include the cyclic groups, the dicyclic groups, and the direct products of two cyclic groups. The polycyclic groups generalize metacyclic groups by allowing more than one level of group extension. A group is polycyclic if it has a ...
The additive group of rational numbers (Q, +) is locally cyclic – any pair of rational numbers a/b and c/d is contained in the cyclic subgroup generated by 1/(bd). [2]The additive group of the dyadic rational numbers, the rational numbers of the form a/2 b, is also locally cyclic – any pair of dyadic rational numbers a/2 b and c/2 d is contained in the cyclic subgroup generated by 1/2 max ...
The theorem also shows that any group of prime order is cyclic and simple, since the subgroup generated by any non-identity element must be the whole group itself. Lagrange's theorem can also be used to show that there are infinitely many primes : suppose there were a largest prime p {\displaystyle p} .
The order of the group () is the product of the orders of the cyclic groups in the direct product. The exponent of the group, that is, the least common multiple of the orders in the cyclic groups, is given by the Carmichael function (sequence A002322 in the OEIS).
One proof is to note that φ(d) is also equal to the number of possible generators of the cyclic group C d ; specifically, if C d = g with g d = 1, then g k is a generator for every k coprime to d. Since every element of C n generates a cyclic subgroup, and each subgroup C d ⊆ C n is generated by precisely φ(d) elements of C n, the formula ...
The index of the normal subgroup not only has to be a divisor of n!, but must satisfy other criteria as well. Since the normal subgroup is a subgroup of H, its index in G must be n times its index inside H. Its index in G must also correspond to a subgroup of the symmetric group S n, the group of permutations of n objects.
If additionally the lattice satisfies the ascending chain condition, then the group is cyclic. Groups whose lattice of subgroups is a complemented lattice are called complemented groups ( Zacher 1953 ), and groups whose lattice of subgroups are modular lattices are called Iwasawa groups or modular groups ( Iwasawa 1941 ).