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A359417 Phi-practical numbers (A260653) whose divisors have distinct values of the Euler totient function (A000010). 3
1, 3, 15, 105, 165, 195, 255, 495, 525, 735, 975, 1155, 1485, 1785, 1815, 1995, 2145, 2415, 2535, 2625, 2805, 3045, 3135, 3255, 3315, 3675, 3705, 3795, 3885, 4305, 4455, 4485, 4515, 4785, 4845, 4875, 4935, 5115, 5145, 5445, 5565, 5655, 5865, 6045, 6105, 6195, 6405 (list; graph; refs; listen; history; text; internal format)
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
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
Intersection of A260653 and A326835.
Cf. A000010.
Sequence in context: A273197 A255427 A181131 * A359418 A354299 A293996
KEYWORD
nonn
AUTHOR
Amiram Eldar, Dec 31 2022
STATUS
approved

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Last modified April 18 22:18 EDT 2024. Contains 371782 sequences. (Running on oeis4.)