OFFSET
1,2
FORMULA
It seems that for n large enough, (1/2)*n*log(n) < a(n) < n*log(n).
MATHEMATICA
Select[Range[137], Divisible @@ Denominator[Sum[{1/k, 1/EulerPhi[k]}, {k, #}]] &] (* Jayanta Basu, Jul 02 2013 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Aug 29 2002
STATUS
approved