A096527 Number of permutations of divisors of n such that all sums of triple adjacent divisors are primes.

0, 0, 0, 6, 0, 0, 0, 12, 6, 4, 0, 12, 0, 4, 4, 4, 0, 0, 0, 16, 12, 0, 0, 20, 6, 4, 12, 20, 0, 0, 0, 0, 4, 4, 24, 48, 0, 4, 12, 50, 0, 0, 0, 4, 12, 0, 0, 0, 0, 0, 0, 16, 0, 0, 24, 136, 12, 4, 0, 286, 0, 0, 96, 0, 24, 0, 0, 30, 0, 0, 0, 0, 0, 0, 32, 16, 4, 0, 0

Offset: 1

Author

Reinhard Zumkeller, Jun 23 2004

Keywords

• nonn

Comments

a(A096530(n)) = 0, a(A096529(n)) > 0.

For square of terms of A053182(n), a(n) = 6. - Michel Marcus, May 08 2014

Examples

			Divisors of n=10 are {1,2,5,10}:
[1,2,10,5]->(1+2+10,2+5+10)=(13,17), [1,10,2,5]->(1+10+2,10+2+5)=(13,17)
[5,2,10,1]->(5+2+10,2+10+1)=(17,13) and
[5,10,2,1]->(5+10+2,10+2+1)=(17,13): therefore a(10)=4.
		

Crossrefs

Cf. A096528, A000005.

Programs

PARI

isokperm(v, nbd, d) = {for (j=1, nbd-2, if (! isprime(d[v[j]] + d[v[j+1]] + d[v[j+2]]), return (0));); return (1);}
a(n) = {d = divisors(n); nbd = #d; if (nbd > 2, sum(i=1, nbd!, isokperm(numtoperm(nbd, i), nbd, d)));} \\ Michel Marcus, May 03 2014

Extensions

More terms from Michel Marcus, May 03 2014