A048969 - OEIS

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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

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OFFSET

1,1

LINKS

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

EXAMPLE

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

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 *)

CROSSREFS

Cf. A000203, A000005, A000043, A048968.

Sequence in context: A093913 A006137 A225269 * A353692 A005564 A011928

Adjacent sequences: A048966 A048967 A048968 * A048970 A048971 A048972

KEYWORD

nice,easy,nonn

AUTHOR

G. L. Honaker, Jr.

EXTENSIONS

More terms from Michel ten Voorde

STATUS

approved