OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
19 is a term since phi(19) = 18, phi(20) = 8, 8*18 = 144 = 12^2.
MATHEMATICA
f[x_] := EulerPhi[x]; Do[s=Sqrt[f[n+1]*f[n]]; If[IntegerQ[s], Print[n]], {n, 1, 5000}]
Position[Partition[EulerPhi[Range[2700]], 2, 1], _?(IntegerQ[GeometricMean[ #]]&), 1, Heads->False]//Flatten (* Harvey P. Dale, Sep 13 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, May 21 2003
STATUS
approved