

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
(list;
graph;
refs;
listen;
history;
text;
internal format)



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

Andrew Howroyd, Table of n, a(n) for n = 1..50


EXAMPLE

From Andrew Howroyd, Aug 26 2017: (Start)
Case n=4: The only cycle is 124.
Case n=6: The 6 cycles are 124, 126, 136, 1362, 13624, 1624.
(End)


CROSSREFS

Sequence in context: A315824 A315825 A328528 * A092297 A294669 A224711
Adjacent sequences: A161784 A161785 A161786 * A161788 A161789 A161790


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



