A066471 Numbers n such that sigma(phi(sigma(n))) = sigma(n).

1, 2, 8, 12, 128, 240, 350, 366, 368, 575, 671, 720, 743, 1098, 2417, 6912, 18967, 19399, 32768, 142560, 173340, 179010, 184032, 188892, 203310, 209628, 225342, 228582, 232160, 244782, 255460, 271072, 274422, 279045, 282285, 287810, 304910, 307612

Offset

1,2

Links

Harry J. Smith and Donovan Johnson, Table of n, a(n) for n = 1..500 (first 250 terms from Harry J. Smith)

Mathematica

Select[Range[1, 10^6], DivisorSigma[1, EulerPhi[DivisorSigma[1, # ]]] == DivisorSigma[1, # ] &]

Prog

(PARI) { n=0; for (m=1, 10^10, if (sigma(eulerphi(sigma(m))) == sigma(m), write("b066471.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Feb 17 2010

Crossrefs

Sequence in context: A272720 A331459 A330816 * A001229 A298640 A120000

Adjacent sequences: A066468 A066469 A066470 * A066472 A066473 A066474

Keyword

nonn

Author

Joseph L. Pe, Jan 02 2002

Status

approved