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a(n) = round(log_2(n)*2^n/n).
2

%I #14 Jun 15 2018 08:10:27

%S 0,2,4,8,15,28,51,96,180,340,644,1224,2332,4456,8535,16384,31515,

%T 60729,117218,226594,438636,850191,1649843,3205121,6232878,12132353,

%U 23636674,46088018,89934782,175624455,343195341,671088640,1313061077

%N a(n) = round(log_2(n)*2^n/n).

%H Harry J. Smith, <a href="/A065617/b065617.txt">Table of n, a(n) for n = 1..200</a>

%t Array[Round[Log2[#]*2^#/#] &, 33] (* _Michael De Vlieger_, Jun 14 2018 *)

%o (PARI) { default(realprecision, 100); t=1/log(2); for (n=1, 200, write("b065617.txt", n, " ", round( t*log(n)*2^n/n)) ) } \\ _Harry J. Smith_, Oct 24 2009

%Y Cf. A065616, A065618.

%K nonn

%O 1,2

%A _N. J. A. Sloane_, Dec 03 2001