A004221 - OEIS

%I #9 Oct 24 2023 23:16:20

%S 0,4,5,7,7,8,9,10,10,10,11,11,12,12,12,13,13,13,13,14,14,14,14,14,14,

%T 15,15,15,15,15,15,16,16,16,16,16,16,16,16,17,17,17,17,17,17,17,17,17,

%U 17,17,18,18,18,18,18,18,18

%N a(n) = ceiling(10*log_10(n)).

%t Ceiling[10*Log[10,Range[60]]] (* _Harvey P. Dale_, Apr 21 2013 *)

%K nonn

%O 1,2

%A _N. J. A. Sloane_