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A067230 Numbers n such that phi(2n-1) = sigma(n). 2
1, 3, 5, 10, 11, 23, 33, 46, 65, 77, 123, 136, 221, 371, 383, 423, 483, 513, 545, 670, 753, 1643, 2033, 3838, 3885, 4533, 4798, 5177, 7463, 7739, 8201, 8985, 9010, 9393, 12256, 13144, 14104, 17110, 17147, 17663, 18695, 19817, 21119, 23038, 24695 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

MATHEMATICA

Select[Range[25000], EulerPhi[2#-1]==DivisorSigma[1, #]&] (* Harvey P. Dale, Aug 22 2015 *)

PROG

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

CROSSREFS

Cf. A000010, A000203, A067229.

Sequence in context: A254540 A326419 A102309 * A321793 A075741 A119133

Adjacent sequences:  A067227 A067228 A067229 * A067231 A067232 A067233

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Feb 20 2002

STATUS

approved

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Last modified January 24 08:03 EST 2022. Contains 350534 sequences. (Running on oeis4.)