A074875 Numbers n such that sigma(sigma(n)-n) = phi(n).

2, 21, 51, 369, 3051, 3783, 5757, 6477, 6897, 7929, 15639, 15925, 20967, 33003, 50739, 58797, 73917, 75627, 118405, 121975, 131979, 170973, 219447, 291369, 310137, 311675, 347337, 365679, 396807, 404559, 437255, 442599, 550719, 558429

Offset

1,1

Links

Donovan Johnson, Table of n, a(n) for n = 1..300

Example

sigma(sigma(21) - 21) = sigma(32 - 21) = sigma(11) = 12 = phi(21), so 21 is a term of the sequence.

Mathematica

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

Crossrefs

Sequence in context: A330201 A042455 A245546 * A231807 A351118 A097718

Adjacent sequences: A074872 A074873 A074874 * A074876 A074877 A074878

Keyword

nonn

Author

Joseph L. Pe, Sep 12 2002

Extensions

a(19)-a(34) from Donovan Johnson, May 13 2010

Status

approved