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Floor(2*n/(3*log(n))).
2

%I #2 Mar 30 2012 18:50:59

%S 1,1,1,2,2,2,2,2,2,3,3,3,3,3,3,4,4,4,4,4,4,4,5,5,5,5,5,5,5,6,6,6,6,6,

%T 6,6,6,7,7,7,7,7,7,7,8,8,8,8,8,8,8,8,9,9,9,9,9,9,9,9,10,10,10,10,10,

%U 10,10,10,10,11,11,11,11,11,11,11,11,12,12,12,12,12,12,12,12,12,13,13,13,13

%N Floor(2*n/(3*log(n))).

%C a(n) <= A000720(n) <= A138195(n), (Tschebyscheff, 1850).

%Y Cf. A050500, A050499, A050501.

%K nonn

%O 2,4

%A _Reinhard Zumkeller_, Mar 04 2008