a(n) = floor(10*log_10(n)).

Terms

a(0) =0a(1) =3a(2) =4a(3) =6a(4) =6a(5) =7a(6) =8a(7) =9a(8) =9a(9) =10a(10) =10a(11) =10a(12) =11a(13) =11a(14) =11a(15) =12a(16) =12a(17) =12a(18) =12a(19) =13a(20) =13a(21) =13a(22) =13a(23) =13a(24) =13a(25) =14a(26) =14a(27) =14a(28) =14a(29) =14