A115918 Numbers k such that sigma(k) - phi(k) is a 4th power.

1, 15, 560, 570, 1071, 1102, 1185, 2035, 2071, 2128, 2185, 3007, 3215, 4087, 4487, 4584, 5406, 9204, 10727, 13912, 16675, 17951, 17970, 19127, 20553, 24288, 24887, 28247, 28290, 30216, 34951, 35807, 35985, 38551, 40967, 44472, 44951, 55247

Offset

1,2

Links

Harvey P. Dale, Table of n, a(n) for n = 1..340

Example

sigma(16675) - phi(16675) = 10000 = 10^4.

Mathematica

fpQ[n_]:=IntegerQ[(DivisorSigma[1, n]-EulerPhi[n])^(1/4)]; Select[Range[ 60000], fpQ] (* Harvey P. Dale, Jun 28 2012 *)

Crossrefs

Cf. A056917, A062385.

Sequence in context: A351183 A061174 A255956 * A110840 A012178 A012229

Adjacent sequences: A115915 A115916 A115917 * A115919 A115920 A115921

Keyword

nonn

Author

Giovanni Resta, Feb 06 2006

Status

approved