OFFSET
1,1
LINKS
Mauro Fiorentini, Table of n, a(n) for n = 1..755 (all terms with n <= 10^9).
EXAMPLE
phi(545) = 3*phi(546) = 432.
MATHEMATICA
Select[Range@ 1000000, EulerPhi@# == 3 EulerPhi[# + 1] &] (* Michael De Vlieger, Apr 12 2015 *)
PROG
(PARI) s=[]; for(n=1, 1000000, if(eulerphi(n)==3*eulerphi(n+1), s=concat(s, n))); s \\ Colin Barker, Apr 12 2015
(Magma) [n: n in [1..2*10^6] | EulerPhi(n) eq 3*EulerPhi(n+1)]; // Vincenzo Librandi, Apr 13 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Mauro Fiorentini, Apr 12 2015
STATUS
approved