A067701 Numbers n such that phi(n-1) + phi(n+1) = phi(2n).

5, 7, 25, 77, 217, 305, 3665, 4645, 5065, 8815, 12205, 12545, 19877, 20435, 24235, 29545, 37735, 47995, 60115, 72085, 73025, 77045, 87475, 121145, 126055, 129245, 149755, 190267, 234635, 247855, 273295, 275723, 419365, 531235, 553475, 621725, 774485, 840085

Offset

1,1

Links

Donovan Johnson, Table of n, a(n) for n = 1..200

Example

phi(25-1) + phi(25+1) = 8+12 = phi(2*25), so 25 is in the sequence.

Mathematica

Select[Range[10^5], EulerPhi[ # - 1] + EulerPhi[ # + 1] == EulerPhi[2# ] &]
Flatten[Position[Partition[EulerPhi[Range[850000]], 3, 1], _?(#[[1]]+#[[3]]== #[[2]]&), 1, Heads->False]]+1 (* Harvey P. Dale, Mar 26 2023 *)

Crossrefs

Cf. A000010, A066231.

Sequence in context: A227922 A179782 A013626 * A059240 A324363 A166100

Adjacent sequences: A067698 A067699 A067700 * A067702 A067703 A067704

Keyword

nonn

Author

Joseph L. Pe, Feb 05 2002

Extensions

Edited by Dean Hickerson, Feb 12 2002

Status

approved