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A109810 Number of permutations of the positive divisors of n, where every element is coprime to its adjacent elements. +0
1
1, 2, 2, 2, 2, 4, 2, 0, 2, 4, 2, 0, 2, 4, 4, 0, 2, 0, 2, 0, 4, 4, 2, 0, 2, 4, 0, 0, 2, 0, 2, 0, 4, 4, 4, 0, 2, 4, 4, 0, 2, 0, 2, 0, 0, 4, 2, 0, 2, 0, 4, 0, 2, 0, 4, 0, 4, 4, 2, 0, 2, 4, 0, 0, 4, 0, 2, 0, 4, 0, 2, 0, 2, 4, 0, 0, 4, 0, 2, 0, 0, 4, 2, 0, 4, 4, 4, 0, 2, 0, 4, 0, 4, 4, 4, 0, 2, 0, 0, 0, 2, 0, 2, 0, 0 (list; graph; listen)
OFFSET

1,2

FORMULA

a(1)=1, a(p) = 2, a(p^2) = 2, a(p*q) = 4 (where p and q are distinct primes), all other terms are 0.

EXAMPLE

The divisors of 6 are 1, 2, 3, and 6. Of the permutations of these integers,

only (6,1,2,3), (6,1,3,2), (2,3,1,6) and (3,2,1,6) are such that every pair of adjacent elements is coprime.

CROSSREFS

Adjacent sequences: A109807 A109808 A109809 this_sequence A109811 A109812 A109813

Sequence in context: A062816 A122857 A132003 this_sequence A122066 A053238 A058263

KEYWORD

nonn,new

AUTHOR

Leroy Quet (qq-quet(AT)mindspring.com), Aug 16 2005

EXTENSIONS

Terms 17 to 59 from Diana Mecum (diana.mecum(AT)gmail.com), Jul 18 2008

More terms from David Wasserman (dwasserm(AT)earthlink.net), Oct 01 2008

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Last modified October 15 09:18 EDT 2008. Contains 145015 sequences.


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