A333741 Odd numbers k such that phi(k) = phi(k+2), where phi is the Euler totient function (A000010).

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

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