A074874 Numbers n such that phi(n + phi(n)) = sigma(n).

1, 3, 5, 11, 23, 55, 87, 123, 383, 501, 957, 1015, 3565, 3777, 5667, 6141, 9069, 11033, 13827, 27347, 35119, 44693, 55645, 91915, 137037, 156919, 180251, 233935, 261989, 269395, 294679, 315605, 335995, 361645, 380103, 389809, 410201, 428399, 443267

Offset

1,2

Links

Donovan Johnson, Table of n, a(n) for n = 1..500

Example

sigma(23) = 24 = phi(23 + 22) = phi(23 + phi(23)), so 23 is a term of the sequence.
phi(87 + phi(87)) = phi(87 + 56) = 120 = sigma(87), so 87 is a member of the sequence.

Mathematica

Select[Range[10^5], EulerPhi[ # + EulerPhi[ # ]] == DivisorSigma[1, # ] &]

Crossrefs

Sequence in context: A094810 A139376 A074892 * A051439 A214873 A330951

Adjacent sequences: A074871 A074872 A074873 * A074875 A074876 A074877

Keyword

nonn

Author

Joseph L. Pe, Sep 12 2002

Status

approved