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

1,4

Comments

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

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

Links

Table of n, a(n) for n=1..79.

Example

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.

Prog

(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

Crossrefs

Cf. A096528, A000005.

Sequence in context: A028704 A028607 A308091 * A028599 A270850 A322379

Adjacent sequences: A096524 A096525 A096526 * A096528 A096529 A096530

Keyword

nonn

Author

Reinhard Zumkeller, Jun 23 2004

Extensions

More terms from Michel Marcus, May 03 2014

Status

approved