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A116040 n+phi(n)+phi(phi(n)) is a triangular number. 4
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 (list; graph; refs; listen; history; text; internal format)
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 A221025 A036666

Adjacent sequences:  A116037 A116038 A116039 * A116041 A116042 A116043

KEYWORD

nonn

AUTHOR

Giovanni Resta, Feb 13 2006

STATUS

approved

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Last modified November 28 22:44 EST 2014. Contains 250441 sequences.