A067229 Numbers n such that phi(2n+1) = sigma(n).

6, 7, 27, 38, 55, 85, 87, 127, 188, 236, 255, 266, 445, 451, 655, 717, 913, 1309, 1357, 1490, 1947, 2095, 2515, 2726, 3002, 3247, 3289, 4117, 4237, 5071, 5605, 7195, 8924, 12128, 12625, 12771, 12837, 13190, 13795, 15835, 16197, 16748, 17997, 20257

Offset

1,1

Links

Donovan Johnson, Table of n, a(n) for n = 1..1000

Mathematica

Select[Range[21000], EulerPhi[2#+1]==DivisorSigma[1, #]&] (* Harvey P. Dale, Sep 06 2024 *)

Prog

(PARI) isok(n) = eulerphi(2*n+1) == sigma(n); \\ Michel Marcus, Nov 21 2013

Crossrefs

Cf. A000010, A000203, A037225, A067230.

Sequence in context: A200179 A054289 A041078 * A291606 A041535 A129214

Adjacent sequences: A067226 A067227 A067228 * A067230 A067231 A067232

Keyword

nonn

Author

Benoit Cloitre, Feb 20 2002

Status

approved