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
Offset: 1
Keywords
Examples
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),
[6,1,2,3,4]->(6+1,1+2,2+3,3+4)=(7,3,5,7) and
[6,1,4,3,2]->(6+1,1+4,4+3,3+2)=(7,5,7,5): therefore a(12)=4.
Comments