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

Author

Amiram Eldar, Apr 03 2020

Keywords

• nonn

Comments

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

Examples

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

Links

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

Crossrefs

Cf. A000010, A001274.

Programs

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 *)