Number of odd nonprimes <= n.

Terms

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