|
|
A272831
|
|
Number of distinct multiplicative groups mod n having 1 as the identity element.
|
|
3
|
|
|
0, 1, 2, 2, 3, 2, 4, 5, 4, 3, 4, 5, 6, 4, 8, 8, 5, 4, 6, 8, 10, 4, 4, 16, 6, 6, 6, 10, 6, 8, 8, 11, 10, 5, 16, 10, 9, 6, 16, 27, 8, 10, 8, 10, 16, 4, 4, 27, 8, 6, 14, 16, 6, 6, 16, 32, 15, 6, 4, 27, 12, 8, 30, 14, 30, 10, 8, 14, 10, 16, 8, 32, 12, 9, 16, 15
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,3
|
|
COMMENTS
|
Equivalently, the number of subgroups of the multiplicative group of integers modulo n. - Andrew Howroyd, Jul 01 2018
Also a(n) is the number of subfields of the n-th cyclotomic field Q(exp(2*Pi*i/n)). - Jianing Song, Feb 12 2021
|
|
LINKS
|
|
|
EXAMPLE
|
For instance a(30) = 8 because only the following 8 groups exist: {1} {1,11} {1,19} {1,7,13,19} {1,17,19,23} {1,29} {1,11,19,29} {1,7,11,13,17,19,23,29}.
|
|
PROG
|
(GAP) Concatenation([0], List([2..80], n->Sum( ConjugacyClassesSubgroups( LatticeSubgroups( GL(1, ZmodnZ(n)))), Size))); # Andrew Howroyd, Jul 01 2018
|
|
CROSSREFS
|
For any identity element, not just 1, see A281365.
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|