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A116040
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n+phi(n)+phi(phi(n)) is a triangular number.
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4
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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
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OFFSET
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1,2
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LINKS
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Harvey P. Dale, Table of n, a(n) for n = 1..1000
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EXAMPLE
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77+phi(77)+phi(phi(77)) = 153 = T(17).
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MATHEMATICA
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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 *)
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CROSSREFS
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Cf. A115905, A116041, A116042, A116043.
Sequence in context: A184863 A162159 A190890 * A218276 A221025 A036666
Adjacent sequences: A116037 A116038 A116039 * A116041 A116042 A116043
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KEYWORD
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nonn
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AUTHOR
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Giovanni Resta, Feb 13 2006
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STATUS
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approved
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