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A349308 Numbers k such that A321167(k) = A321167(k+1) > 1. 3
80, 135, 296, 343, 375, 624, 728, 1160, 1431, 1592, 1624, 2240, 2295, 2456, 2511, 2624, 2727, 2888, 3429, 3591, 3624, 3752, 3992, 4023, 4184, 4671, 4887, 4913, 5048, 5144, 5264, 5319, 5480, 5696, 6183, 6344, 6375, 6591, 6615, 6776, 6858, 6859, 7479, 7624, 7640 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Without the restriction that A321167(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 6858, 13375, 22625, ...
LINKS
EXAMPLE
80 is a term since A321167(80) = A321167(81) = 3.
MATHEMATICA
f[p_, e_] := p^e - 1; uphi[1] = 1; uphi[n_] := Times @@ f @@@ FactorInteger[n]; fe[p_, e_] := uphi[e]; euphi[n_] := Times @@ fe @@@ FactorInteger[n]; Select[Range[8000], euphi[#] == euphi[# + 1] > 1 &]
CROSSREFS
Subsequence of A068140.
Similar sequences: A001274, A287055, A293184, A326403, A349307.
Sequence in context: A068140 A365867 A349307 * A224547 A204648 A202447
KEYWORD
nonn
AUTHOR
Amiram Eldar, Nov 14 2021
STATUS
approved

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Last modified March 29 08:49 EDT 2024. Contains 371268 sequences. (Running on oeis4.)