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A161787
Number of (undirected) cycles in the graph with nodes labeled 1..n, and nodes i and j joined by an edge if i divides j or vice versa.
1
0, 0, 0, 1, 1, 6, 6, 18, 25, 42, 42, 241, 241, 324, 667, 1602, 1602, 5511, 5511, 21596, 32549, 35434, 35434, 237727, 270992, 292057, 421656, 1140425, 1140425, 7609789, 7609789, 19163336, 22436043, 23293234, 46391754, 313698907, 313698907, 324745136, 370720970, 2113744875
OFFSET
1,6
COMMENTS
Old definition was "Number of unique loops in a map of 1 to N vertices, with nondirectional connections between vertices which are factors or multiples of each other".
LINKS
EXAMPLE
From Andrew Howroyd, Aug 26 2017: (Start)
Case n=4: The only cycle is 1-2-4.
Case n=6: The 6 cycles are 1-2-4, 1-2-6, 1-3-6, 1-3-6-2, 1-3-6-2-4, 1-6-2-4.
(End)
CROSSREFS
Sequence in context: A315824 A315825 A328528 * A342285 A092297 A294669
KEYWORD
nonn,obsc
AUTHOR
David Eaton (dave(AT)suave.net), Jun 19 2009
EXTENSIONS
Partially edited by N. J. A. Sloane, Dec 21 2014
Name clarified, a(21) corrected and a(25)-a(40) from Andrew Howroyd, Aug 26 2017
STATUS
approved