A349307 Numbers k such that A072911(k) = A072911(k+1) > 1.

80, 135, 296, 343, 375, 567, 624, 728, 783, 944, 1160, 1431, 1592, 1624, 1647, 1808, 1863, 2024, 2240, 2295, 2456, 2511, 2624, 2727, 2888, 3087, 3320, 3429, 3536, 3591, 3624, 3752, 3992, 4023, 4184, 4239, 4375, 4400, 4455, 4624, 4671, 4887, 4912, 4913, 5048, 5103

Offset

1,1

Comments

Without the restriction that A072911(k) > 1, all the terms of A340152 would be in this sequence.

In contrast to A001274, which has only one known pair of consecutive terms (5186 and 5187), this sequence seems to have many pairs of consecutive terms. The smaller members of these pairs are 4912, 5750, 6858, ...

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

80 is a term since A072911(80) = A072911(81) = 2.

Mathematica

f[p_, e_] := EulerPhi[e]; ephi[n_] := Times @@ f @@@ FactorInteger[n]; Select[Range[5000], ephi[#] == ephi[# + 1] > 1 &]

Crossrefs

Cf. A072911, A340152.

Subsequence of A068140.

Similar sequences: A001274, A287055, A293184, A326403, A349308.

Sequence in context: A261549 A068140 A365867 * A349308 A224547 A204648

Adjacent sequences: A349304 A349305 A349306 * A349308 A349309 A349310

Keyword

nonn

Author

Amiram Eldar, Nov 14 2021

Status

approved