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A066930

Numbers k such that phi(sigma(k)) divides sigma(phi(k)).

1, 7, 9, 29, 71, 97, 109, 121, 139, 142, 175, 183, 194, 215, 225, 242, 244, 261, 278, 311, 344, 349, 355, 430, 497, 509, 516, 533, 556, 571, 605, 622, 631, 647, 673, 709, 729, 791, 817, 859, 911, 923, 1021, 1066, 1112, 1119, 1142, 1207, 1243, 1262, 1277

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harry J. Smith)

MATHEMATICA

Select[Range[1300], Divisible[DivisorSigma[1, EulerPhi[#]], EulerPhi[ DivisorSigma[ 1, #]]]&] (* Harvey P. Dale, Dec 15 2021 *)

PROG

(PARI) isok(k) = { sigma(eulerphi(k)) % eulerphi(sigma(k)) == 0 } \\ Harry J. Smith, Apr 08 2010

CROSSREFS

Cf. A000010 (phi), A000203 (sigma), A033632 (subsequence), A062401, A062402.

Sequence in context: A030404 A242505 A263826 * A247192 A154260 A309199