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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

Table of n, a(n) for n=1..27.

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 *)

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 A198483 A115735

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 January 21 13:38 EST 2018. Contains 297994 sequences.