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

1,6

COMMENTS

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

LINKS

Table of n, a(n) for n=1..23.

S. Sykora, On Neighbor-Property 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

STATUS

approved

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Last modified May 22 16:19 EDT 2017. Contains 286882 sequences.