A096158 - OEIS

A096158

Number of permutations of proper divisors of n such that the sum of adjacent pairs of divisors is prime.

0, 0, 0, 2, 0, 2, 0, 2, 0, 2, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

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OFFSET

1,4

COMMENTS

For n>4: a(n)=2 iff (n/2,2+n/2) is twin prime pair, a(2*A001359(n))=2;

a(A096160(n)) > 0.

LINKS

Table of n, a(n) for n=1..102.

EXAMPLE

Proper divisors of n=12 are {1,2,3,4,6}:

[2,3,4,1,6]->(2+3,3+4,4+1,1+6)=(5,7,5,7),

[4,3,2,1,6]->(4+3,3+2,2+1,1+6)=(7,5,3,7),