A066231 Numbers n such that phi(n) = phi(n-1) - phi(n-2).

6, 8, 26, 78, 218, 306, 3666, 4646, 5066, 8816, 12206, 12546, 19878, 20436, 24236, 29546, 37736, 47996, 60116, 72086, 73026, 77046, 87476, 121146, 126056, 129246, 149756, 190268, 234636, 247856, 273296, 275724, 419366, 531236, 553476, 621726

Offset

1,1

Comments

Question: Are all terms of this sequence even? (Compare A065557, whose terms could be all odd and squarefree.)

Links

Harry J. Smith and Jud McCranie, Table of n, a(n) for n = 1..494 (first 117 terms from Harry J. Smith)

Example

phi(8) = 4 = 6-2 = phi(7) - phi(6).

Mathematica

Flatten[Position[Partition[EulerPhi[Range[630000]], 3, 1], _?(#[[3]] == #[[2]]- #[[1]]&), 1, Heads->False]]+2 (* Harvey P. Dale, Aug 19 2018 *)

Prog

(PARI) n=0; for (m=3, 10^9, if (eulerphi(m) == eulerphi(m - 1) - eulerphi(m - 2), write("b066231.txt", n++, " ", m); if (n==117, return)) ) \\ Harry J. Smith, Feb 06 2010

Crossrefs

Cf. A066232, A067701.

Sequence in context: A219191 A107366 A024873 * A267477 A237290 A229335

Adjacent sequences: A066228 A066229 A066230 * A066232 A066233 A066234

Keyword

nonn

Author

Joseph L. Pe, Dec 18 2001

Extensions

a(24)-a(36) from Harry J. Smith, Feb 06 2010

Status

approved