A048969 Composite numbers k such that sigma(k) / d(k) is prime.

6, 20, 45, 49, 150, 169, 361, 832, 961, 1445, 1734, 1849, 5329, 8405, 9409, 9477, 10086, 10609, 14580, 14641, 16129, 17405, 20886, 24649, 25205, 30246, 39601, 39605, 47526, 49729, 51005, 58081, 61206, 73441, 85805, 102966, 139445, 149645, 167281, 167334

Offset: 1

Author

G. L. Honaker, Jr.

Keywords

• nice
• easy
• nonn

Examples

			For k=6 (composite), sigma(6)=12, d(6)=4 and 12/4 = 3 is prime.
		

Links

• Donovan Johnson, Table of n, a(n) for n = 1..1000 (first 259 terms from T. D. Noe)

Crossrefs

Cf. A000203, A000005, A000043, A048968.

Programs

Mathematica

nn=62000;With[{comps=Complement[Range[nn],Prime[Range[PrimePi[nn]]]]}, Select[ comps, PrimeQ[DivisorSigma[1,#]/DivisorSigma[0,#]]&]] (* Harvey P. Dale, Feb 19 2012 *)

Extensions

More terms from Michel ten Voorde