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A066589
Let u_n be the group of units mod n (invertible elements in the ring Z_n); a(n) is the number of cyclic subgroups in u_n.
1
1, 1, 2, 2, 3, 2, 4, 4, 4, 3, 4, 4, 6, 4, 6, 6, 5, 4, 6, 6, 8, 4, 4, 8, 6, 6, 6, 8, 6, 6, 8, 8, 8, 5, 12, 8, 9, 6, 12, 12, 8, 8, 8, 8, 12, 4, 4, 12, 8, 6, 10, 12, 6, 6, 12, 16, 12, 6, 4, 12, 12, 8, 20, 10, 20, 8, 8, 10, 8, 12, 8, 16, 12, 9, 12, 12, 16, 12, 8, 20
OFFSET
1,3
LINKS
PROG
(GAP) List([1..80], n->Sum( ConjugacyClasses( AutomorphismGroup( CyclicGroup(n))), x->Size(x)/Phi(Order( Representative(x)))));
(PARI) a(n)={sum(i=1, n, if(gcd(i, n)==1, 1/eulerphi(znorder(Mod(i, n)))))} \\ Andrew Howroyd, Jul 01 2018
CROSSREFS
Sequence in context: A334968 A124771 A334299 * A007897 A180783 A290731
KEYWORD
nonn
AUTHOR
Sharon Sela (sharonsela(AT)hotmail.com), Jan 08 2002
EXTENSIONS
a(32)-a(33) inserted and terms a(37) and beyond from Andrew Howroyd, Jul 01 2018
STATUS
approved