|
%I #5 Nov 21 2013 12:48:48
%S 1,3,7,16,22,23,24,46,50,54,57,67,77,81,109,135,164,204,273,304,311,
%T 331,391,415,438,500,532,541,671,685,690,702,783,855,1025,1130,1264,
%U 1301,1375,1459,1603,1667,1707,1775,1864,1953,2053,2055,2136,2369
%N n+phi(n)+phi(phi(n)) is a triangular number.
%H Harvey P. Dale, <a href="/A116040/b116040.txt">Table of n, a(n) for n = 1..1000</a>
%e 77+phi(77)+phi(phi(77)) = 153 = T(17).
%t 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 *)
%Y Cf. A115905, A116041, A116042, A116043.
%K nonn
%O 1,2
%A _Giovanni Resta_, Feb 13 2006
|
