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A117541
Number of permutations P of 1..n such that in P and in the inverse of P, every pair of adjacent numbers are relatively prime.
1
1, 2, 6, 9, 56, 23, 399, 442, 2220, 2386, 71577, 22001, 1179483, 1156519, 4975079
OFFSET
1,2
COMMENTS
Sequence suggested by Leroy Quet on the SeqFan mailing list.
EXAMPLE
a(4)=9, since the 9 permutations (1,2,3,4), (1,4,3,2), (2,1,3,4), (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
Sequence in context: A101713 A240761 A342317 * A244060 A333185 A236106
KEYWORD
nonn
AUTHOR
Giovanni Resta, Mar 28 2006
STATUS
approved