OFFSET
1,2
COMMENTS
A phi-practical number k is a number k such that each number in the range 1..k is a subsum of a the multiset {phi(d) : d | k}. This sequence is restricted to cases in which all the values in this multiset are distinct.
Are all the terms above 3 divisible by 5?
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
phiPracticalQ[n_] := If[n<1, False, 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)]]; (* Frank M Jackson's code at A260653 *)
Select[Range[40000], UnsameQ @@ EulerPhi[Divisors[#]] && phiPracticalQ[#] &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Dec 31 2022
STATUS
approved