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A117542
Number of permutations P of 1..n such that in P and in the inverse of P, every pair of adjacent numbers and the first and last number, are relatively prime.
1
1, 2, 6, 8, 36, 16, 127, 320, 581, 1564, 13565, 13760, 149186, 773727, 540538
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OFFSET
1,2
COMMENTS
Sequence suggested by
Leroy Quet
on the SeqFan mailing list.
LINKS
Table of n, a(n) for n=1..15.
EXAMPLE
a(4)=8, since the 8 permutations (1,2,3,4), (1,4,3,2), (2,1,4,3), (2,3,4,1), (4,1,2,3), (3,2,1,4), (3,4,1,2), (4,3,2,1) satisfy the property.
CROSSREFS
Cf.
A076220
,
A117541
.
Sequence in context:
A019199
A094678
A076507
*
A045653
A235320
A152158
Adjacent sequences:
A117539
A117540
A117541
*
A117543
A117544
A117545
KEYWORD
nonn
AUTHOR
Giovanni Resta
, Mar 28 2006
STATUS
approved
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Last modified April 24 22:17 EDT 2024. Contains 371964 sequences. (Running on oeis4.)