A065817 Numbers n such that sigma_5(n)/sigma_1(n) is prime.

2, 3, 4, 5, 9, 11, 37, 43, 47, 71, 121, 131, 157, 223, 251, 257, 289, 307, 487, 529, 641, 1087, 1093, 1187, 1291, 1433, 1567, 1621, 1637, 1831, 1849, 1873, 1901, 2017, 2111, 2143, 2293, 2333, 2473, 2621, 2663, 2683, 2707, 2777, 2809, 2843, 2903, 3257, 3413

Offset

1,1

Links

Harry J. Smith, Table of n, a(n) for n=1..1000

Mathematica

Select[Range[1, 3000 ], PrimeQ[( DivisorSigma[5, # ])/DivisorSigma[1, # ]] & ]

Prog

(PARI) { n=0; for (m=1, 10^9, f=sigma(m, 5)/sigma(m); if (frac(f) == 0 && isprime(f), write("b065817.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Oct 31 2009

Crossrefs

Sequence in context: A333612 A362025 A093305 * A361227 A084542 A038201

Adjacent sequences: A065814 A065815 A065816 * A065818 A065819 A065820

Keyword

nonn

Author

Robert G. Wilson v, Dec 06 2001

Status

approved