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 A178254 Number of permutations of the proper divisors of n such that no adjacent elements have a common divisor greater than 1. 8

%I

%S 1,1,1,2,1,6,1,2,2,6,1,4,1,6,6,0,1,4,1,4,6,6,1,0,2,6,2,4,1,36,1,0,6,6,

%T 6,0,1,6,6,0,1,36,1,4,4,6,1,0,2,4,6,4,1,0,6,0,6,6,1,0,1,6,4,0,6,36,1,

%U 4,6,36,1,0,1,6,4,4,6,36,1,0,0,6,1,0,6,6,6,0,1,0,6,4,6,6,6,0,1,4,4,0,1,36,1

%N Number of permutations of the proper divisors of n such that no adjacent elements have a common divisor greater than 1.

%C Depends only on prime signature;

%C range = {0, 1, 2, 4, 6, 36};

%C a(A033987(n)) = 0; a(A037144(n)) > 0;

%C a(A008578(n))=1; a(A168363(n))=2; a(A054753(n))=4; a(A006881(n))=6; a(A007304(n))=36.

%H R. Zumkeller, <a href="/A178254/b178254.txt">Table of n, a(n) for n = 1..10000</a>

%H R. Zumkeller, <a href="/A178254/a178254.txt">Example: n=42</a>

%e Proper divisors for n=21 are: 1, 3, and 7:

%e a(39) = #{[1,3,7], [1,7,3], [3,1,7], [3,7,1], [7,1,3], [7,3,1]} = 6;

%e proper divisors for n=12 are: 1, 2, 3, 4, and 6:

%e a(12) = #{[2,3,4,1,6], [4,3,2,1,6], [6,1,2,3,4], [6,1,4,3,2]} = 4;

%e proper divisors for n=42: 1, 2, 3, 6, 7, 14, and 21:

%e a(42) = #{[2,21,1,6,7,3,14], [2,21,1,14,3,7,6], [3,14,1,6,7,2,21], [3,14,1,21,2,7,6], [6,1,14,3,7,2,21], [6,1,21,2,7,3,14], ...} = 36, see the appended file for the list of all permutations.

%Y Cf. A109810.

%K nonn

%O 1,4

%A _Reinhard Zumkeller_, May 24 2010

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Last modified July 30 03:08 EDT 2021. Contains 346347 sequences. (Running on oeis4.)