A065820 Numbers n such that sigma_6(n)/sigma_2(n) is prime.

2, 3, 5, 13, 17, 31, 43, 61, 83, 109, 131, 229, 239, 257, 263, 269, 311, 313, 443, 463, 503, 571, 593, 599, 619, 641, 647, 653, 659, 701, 797, 811, 853, 953, 967, 1009, 1031, 1039, 1063, 1123, 1373, 1459, 1483, 1499, 1663, 1669, 1693, 1733, 1741, 1759, 1789

Offset

1,1

Links

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

Example

All entries are themselves prime.

Mathematica

Select[Range[1, 2000 ], PrimeQ[( DivisorSigma[6, # ])/DivisorSigma[2, # ]] & ]

Prog

(PARI) { n=0; for (m=1, 10^9, f=sigma(m, 6)/sigma(m, 2); if (frac(f) == 0 && isprime(f), write("b065820.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Oct 31 2009

Crossrefs

Sequence in context: A154554 A105879 A066111 * A163268 A235624 A355518

Adjacent sequences: A065817 A065818 A065819 * A065821 A065822 A065823

Keyword

nonn

Author

Robert G. Wilson v, Dec 06 2001

Status

approved