

A242531


Number of cyclic arrangements of S={1,2,...,n} such that the difference of any two neighbors is a divisor of their sum.


15



0, 1, 1, 1, 1, 4, 3, 9, 26, 82, 46, 397, 283, 1675, 9938, 19503, 10247, 97978, 70478, 529383, 3171795, 7642285, 3824927, 48091810, 116017829, 448707198, 1709474581, 6445720883
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OFFSET

1,6


COMMENTS

a(n)=NPC(n;S;P) is the count of all neighborproperty cycles for a specific set S of n elements and a specific pairproperty P. For more details, see the link and A242519.


LINKS

Table of n, a(n) for n=1..28.
S. Sykora, On NeighborProperty Cycles, Stan's Library, Volume V, 2014.


EXAMPLE

The only such cycle of length n=5 is {1,2,4,5,3}.
For n=7 there are three solutions: C_1={1,2,4,5,7,6,3}, C_2={1,2,4,6,7,5,3}, C_3={1,2,6,7,5,4,3}.


PROG

(C++) See the link.


CROSSREFS

Cf. A242519, A242520, A242521, A242522, A242523, A242524, A242525, A242526, A242527, A242528, A242529, A242530, A242532, A242533, A242534.
Sequence in context: A103218 A107381 A062882 * A275160 A132192 A147756
Adjacent sequences: A242528 A242529 A242530 * A242532 A242533 A242534


KEYWORD

nonn,hard,more


AUTHOR

Stanislav Sykora, May 30 2014


EXTENSIONS

a(24)a(28) from Fausto A. C. Cariboni, May 25 2017


STATUS

approved



