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
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 13 2006
STATUS
approved