OFFSET
1,1
EXAMPLE
phi(976^2) = 468480 = 480*976 = phi(975)*phi(977).
MATHEMATICA
Select[Range[10^6], EulerPhi[#^2] == EulerPhi[# - 1] EulerPhi[# + 1] &]
PROG
(PARI) isok(n) = eulerphi(n^2) == eulerphi(n-1) * eulerphi(n+1); \\ Michel Marcus, Aug 12 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Carl Najafi, Dec 06 2012
EXTENSIONS
More terms from Amiram Eldar, Aug 12 2019
STATUS
approved