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A092272 Numbers n such that phi(n) = phi(2*n+1). 2
97, 1417, 2593, 107167, 128137, 262993, 468247, 629821, 879937, 894127, 1100347, 1260847, 1620307, 1644967, 1897417, 2890717, 3122773, 3186397, 3651667, 4169197, 6176467, 7072477, 7344187, 8237707, 8974717, 9254647, 13032547, 15540037, 15673027 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..200

EXAMPLE

phi(97) = 97-1 = 96 = 2*4*12 = phi(3*5*13) = phi(195) = phi(2*97+1)

MAPLE

with (numtheory): for i from 1 to 1000000 do if phi(i)=phi(2*i+1) then print(i) fi; od;

MATHEMATICA

Do[ If[ EulerPhi[n] == EulerPhi[2n + 1], Print[n]], {n, 1, 15540036}] (* Robert G. Wilson v, Feb 20 2004 *)

PROG

(PARI) is(n)=my(t=eulerphi(2*n+1)); t<n && t==eulerphi(n) \\ Charles R Greathouse IV, May 19 2013

CROSSREFS

Cf. A000010, A005384.

Sequence in context: A224106 A038532 A226082 * A233433 A162542 A241968

Adjacent sequences:  A092269 A092270 A092271 * A092273 A092274 A092275

KEYWORD

nonn

AUTHOR

Pooya Farshim (P.Farshim.00(AT)cantab.net), Feb 17 2004

EXTENSIONS

More terms from Labos Elemer and Robert G. Wilson v, Feb 19 2004

STATUS

approved

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Last modified December 6 14:15 EST 2019. Contains 329806 sequences. (Running on oeis4.)