A066232 Numbers n such that phi(n) = phi(n-2) - phi(n-1).

195, 3531, 9339, 27231, 46795, 78183, 90195, 112995, 135015, 437185, 849405, 935221, 1078581, 1283601, 1986975, 2209585, 2341185, 2411175, 2689695, 2744145, 3619071, 3712545, 4738185, 5132985, 6596121, 7829031, 8184715, 12176109

Offset

1,1

Comments

As in A065557, all terms listed here are odd. Problem: Prove that this holds in general.

Links

Harry J. Smith and Jud McCranie, Table of n, a(n) for n = 1..289 (first 55 terms from Harry J. Smith)

Example

Phi(195) = 96 = 192-96 = phi(193)-phi(194).

Mathematica

Select[Range[3, 10^6], EulerPhi[ # ] == EulerPhi[ # - 2] - EulerPhi[ # - 1] &]

Prog

(PARI) { n=0; for (m=3, 10^9, if (eulerphi(m) == eulerphi(m - 2) - eulerphi(m - 1), write("b066232.txt", n++, " ", m); if (n==100, return)) ) } \\ Harry J. Smith, Feb 07 2010

Crossrefs

Cf. A066231, A067701.

Sequence in context: A295130 A257765 A259694 * A284960 A226105 A164130

Adjacent sequences: A066229 A066230 A066231 * A066233 A066234 A066235

Keyword

nonn

Author

Joseph L. Pe, Dec 18 2001

Extensions

a(13)-a(28) from Harry J. Smith, Feb 07 2010

Status

approved