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a(n) = floor(10*log(n)).
3

%I #14 Jan 03 2022 21:27:07

%S 0,6,10,13,16,17,19,20,21,23,23,24,25,26,27,27,28,28,29,29,30,30,31,

%T 31,32,32,32,33,33,34,34,34,34,35,35,35,36,36,36,36,37,37,37,37,38,38,

%U 38,38,38,39,39,39,39,39,40,40,40,40,40,40,41,41,41,41,41,41

%N a(n) = floor(10*log(n)).

%H Vincenzo Librandi, <a href="/A004234/b004234.txt">Table of n, a(n) for n = 1..10000</a>

%e a(2) = 6 because 10*log(2) = 6.9314718...

%e a(3) = 10 because 10*log(3) = 10.9861228...

%e a(4) = 13 because 10*log(4) = 13.8629436...

%t Table[Floor[10Log[n]], {n, 75}] (* _Alonso del Arte_, Dec 24 2013 *)

%Y Cf. A004219.

%K nonn,easy

%O 1,2

%A _N. J. A. Sloane_

%E More terms from _Alonso del Arte_, Dec 24 2013