a(n) = ceiling(log(n)).

Terms

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