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A328857 Numbers with a record number of divisors that have the same value of the Euler totient function (A000010). 0
1, 2, 12, 120, 240, 2520, 10920, 21840, 32760, 65520, 600600, 900900, 1801800, 3603600, 4455360, 8910720, 17821440, 46060560, 69090840, 92121120, 126977760, 138181680, 245044800, 414545040, 490089600, 507911040, 1015822080, 1266665400, 1523733120, 2533330800 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The corresponding record values are 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 13, 14, 16, 17, 18, 20, 21, 23, 24, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, 36, ...

LINKS

Table of n, a(n) for n=1..30.

EXAMPLE

2 has 2 divisors with the same value of phi: phi(1) = phi(2) = 1.

12 has 3 divisors with the same value of phi: phi(3) = phi(4) = phi(6) = 2.

MATHEMATICA

f[n_] := Max[Tally[EulerPhi /@ Divisors[n]][[;; , 2]]]; fm = 0; s = {}; Do[f1 = f[n]; If[f1 > fm, fm = f1; AppendTo[s, n]], {n, 1, 10^6}]; s

CROSSREFS

Cf. A000010, A102190.

Sequence in context: A305051 A274305 A317013 * A295864 A255506 A095717

Adjacent sequences:  A328854 A328855 A328856 * A328858 A328859 A328860

KEYWORD

nonn

AUTHOR

Amiram Eldar, Oct 28 2019

STATUS

approved

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Last modified October 25 17:13 EDT 2021. Contains 348255 sequences. (Running on oeis4.)