OFFSET
1,2
COMMENTS
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(3) = 18 is in the sequence because psi(phi(18)) = phi(psi(18)) = 12 but psi(phi(9)) = 12 <> 4 = phi(psi(9)).
MAPLE
MATHEMATICA
f[n_] := n Sum[MoebiusMu[d]^2/d, {d, Divisors@ n}]; With[{s = Select[Range[3000], f[EulerPhi@ #] == EulerPhi[f@ #] &]}, Select[s, FreeQ[s, #/2] &]] (* Michael De Vlieger, Sep 06 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel, Sep 06 2017
STATUS
approved