OFFSET
1,1
COMMENTS
The squarefree numbers (A005117) are excluded from this sequence since every squarefree phi-practical number is also a unitary phi-practical number.
The least odd term in this sequence is a(104) = 8085.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
phiPracticalQ[n_] := If[n == 1, True, (lst = Sort @ EulerPhi @ Divisors[n]; ok = True; Do[If[lst[[m]] > Sum[lst[[l]], {l, 1, m - 1}] + 1, (ok = False; Break[])], {m, 1, Length[lst]}]; ok)];
uphi[n_] := If[n == 1, 1, (Times @@ (Table[#[[1]]^#[[2]] - 1, {1}] & /@ FactorInteger[n]))[[1]]];
uDivisors[n_] := Select[Divisors[n], GCD[#, n/#] == 1 &];
uPhiPracticalQ[n_] := If[n < 1, False, If[n == 1, True, (lst = Sort@Map[uphi, uDivisors[n]]; ok = True; Do[If[lst[[m]] > Sum[lst[[l]], {l, 1, m - 1}] + 1, (ok = False; Break[])], {m, 1, Length[lst]}]; ok)]]; (* Frank M Jackson's code at A260653 *)
Select[Range[3200], ! SquareFreeQ[#] && phiPracticalQ[#] && uPhiPracticalQ[#] &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Dec 31 2022
STATUS
approved