OFFSET
1,1
COMMENTS
For k less than 4*10^6, k is prime, semiprime, or triprime (3-almost prime).
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..289 (calculated using the b-file at A066232)
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
KEYWORD
nonn
AUTHOR
Antonio Roldán, Oct 10 2011
EXTENSIONS
a(27) from Vincenzo Librandi, Sep 27 2013
STATUS
approved