OFFSET
1,4
COMMENTS
For square of terms of A053182(n), a(n) = 6. - Michel Marcus, May 08 2014
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
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jun 23 2004
EXTENSIONS
More terms from Michel Marcus, May 03 2014
STATUS
approved