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 A197112 Numbers n such that phi(n) = phi(n+1) + phi(n+2). 1
 193, 3529, 9337, 27229, 46793, 78181, 90193, 112993, 135013, 437183, 849403, 935219, 1078579, 1283599, 1986973, 2209583, 2341183, 2411173, 2689693, 2744143, 3619069, 3712543, 4738183, 5132983, 6596119, 7829029, 8184713 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For n less than 4*10^6, n is prime, semiprime, or triprime (3-almost prime). LINKS FORMULA a(n) = A066232(n)-2. - Donovan Johnson, Oct 14 2011 EXAMPLE 112993 is in the sequence, because phi(112993)=106704, phi(112994)=48384, phi(112995)=58320  and 106704=48384+58320. MAPLE for k from 0 do         if numtheory[phi](k) = numtheory[phi](k+1)+numtheory[phi](k+2) then                 printf("%d\n", k) ;         end if; end do: # R. J. Mathar, Oct 13 2011 MATHEMATICA Select[Range[10^5], EulerPhi[#] == EulerPhi[# + 1] + EulerPhi[# + 2] &] (* Alonso del Arte, Oct 13 2011 *) Position[Partition[EulerPhi[Range[82*10^5]], 3, 1], _?(#[[1]]==#[[2]]+#[[3]]&), 1, Heads->False]//Flatten (* Harvey P. Dale, May 10 2022 *) PROG (PARI) isok(n) = eulerphi(n) == eulerphi(n+1) + eulerphi(n+2); \\ Michel Marcus, May 15 2016 CROSSREFS Cf. A092404. Sequence in context: A178265 A201112 A250156 * A120851 A302332 A344147 Adjacent sequences:  A197109 A197110 A197111 * A197113 A197114 A197115 KEYWORD nonn AUTHOR Antonio Roldán, Oct 10 2011 EXTENSIONS a(27) from Vincenzo Librandi, Sep 27 2013 STATUS approved

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Last modified August 7 23:50 EDT 2022. Contains 355995 sequences. (Running on oeis4.)