A116040 n+phi(n)+phi(phi(n)) is a triangular number.

1, 3, 7, 16, 22, 23, 24, 46, 50, 54, 57, 67, 77, 81, 109, 135, 164, 204, 273, 304, 311, 331, 391, 415, 438, 500, 532, 541, 671, 685, 690, 702, 783, 855, 1025, 1130, 1264, 1301, 1375, 1459, 1603, 1667, 1707, 1775, 1864, 1953, 2053, 2055, 2136, 2369

Offset

1,2

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

77+phi(77)+phi(phi(77)) = 153 = T(17).

Mathematica

tnoQ[n_]:=Module[{eph=EulerPhi[n]}, IntegerQ[(Sqrt[8(n+eph+ EulerPhi[ eph])+ 1 ]-1)/2]]; Select[Range[2500], tnoQ] (* Harvey P. Dale, Oct 01 2011 *)

Crossrefs

Cf. A115905, A116041, A116042, A116043.

Sequence in context: A184863 A162159 A190890 * A218276 A373334 A221025

Adjacent sequences: A116037 A116038 A116039 * A116041 A116042 A116043

Keyword

nonn

Author

Giovanni Resta, Feb 13 2006

Status

approved