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A333741 Odd numbers k such that phi(k) = phi(k+2), where phi is the Euler totient function (A000010). 2
7, 635, 1015, 2695, 6497, 10307, 12317, 13445, 46205, 77693, 81303, 133787, 134995, 151823, 162925, 180633, 181427, 220113, 288925, 359905, 392819, 404471, 439097, 453167, 485237, 682649, 739023, 840851, 879303, 910195, 988713, 1392317, 1410119, 1434895, 1503347 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The odd terms of A001494. These terms are relatively rare: of the first 10000 terms of A001494 only 63 are odd.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..1000

EXAMPLE

7 is a term since phi(7) = phi(9) = 6.

MATHEMATICA

Select[Range[1, 10^6, 2], EulerPhi[#] == EulerPhi[# + 2] &]

2#-1&/@SequencePosition[EulerPhi[Range[1, 151*10^4, 2]], {x_, x_}][[All, 1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 15 2020 *)

CROSSREFS

Cf. A000010, A001274.

Sequence in context: A047942 A319033 A182346 * A175601 A246113 A277839

Adjacent sequences:  A333738 A333739 A333740 * A333742 A333743 A333744

KEYWORD

nonn

AUTHOR

Amiram Eldar, Apr 03 2020

STATUS

approved

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Last modified January 19 22:12 EST 2022. Contains 350466 sequences. (Running on oeis4.)