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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

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