a(n) = floor(n/9)*ceiling(n/9).

Terms

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