OFFSET
1,1
COMMENTS
If m is a term in A051674, then m'' = m, phi(m'') = phi(m) so the sequence is infinite.
EXAMPLE
phi(4'') = phi(4) because 4'' = 4, so 4 is a term.
phi (27'') = phi(27) because 27'' = 27, so 27 is a term.
phi(104'') = phi(164') = phi(168) = phi (8*3*7) = 4*2*6 = 48 and phi(104) = phi(8*13) = 4*12 = 48, so 104 is a term.
MATHEMATICA
d[0] = d[1] = 0; d[n_] := n * Plus @@ ((Last[#]/First[#]) & /@ FactorInteger[n]); Select[Range[25000], EulerPhi[#] == EulerPhi[d[d[#]]] &] (* Amiram Eldar, Apr 10 2022 *)
PROG
(Magma) f:=func<n |n le 1 select 0 else n*(&+[Factorisation(n)[i][2] / Factorisation(n)[i][1]: i in [1..#Factorisation(n)]])>; [n:n in [2..24300]| not IsPrime(n) and EulerPhi(n) eq EulerPhi(Floor(f(Floor(f(n))))) ];
CROSSREFS
KEYWORD
nonn
AUTHOR
Marius A. Burtea, Apr 09 2022
STATUS
approved