A065523 Numbers n such that sigma(n) is a prime power (A025475).

3, 7, 21, 31, 81, 93, 127, 217, 381, 400, 651, 889, 2667, 3937, 8191, 11811, 24573, 27559, 57337, 82677, 131071, 172011, 253921, 393213, 524287, 761763, 917497, 1040257, 1572861, 1777447, 2752491, 3120771, 3670009, 4063201, 5332341

Offset

1,1

Links

Donovan Johnson, Table of n, a(n) for n = 1..80

Mathematica

s[n_] := DivisorSigma[1, n ]; Select[ Range[2, 10^6], !PrimeQ[ s[ # ]] && Mod[ s[ # ], s[ # ] - EulerPhi[ s[ # ]]] == 0 & ]

Crossrefs

A proper subset of A065496.

Sequence in context: A003585 A108102 A357898 * A046528 A018572 A018641

Adjacent sequences: A065520 A065521 A065522 * A065524 A065525 A065526

Keyword

nonn

Author

Robert G. Wilson v, Nov 27 2001

Extensions

a(31)-a(35) from Donovan Johnson, Sep 05 2008

Status

approved