a(n) = ceiling(sqrt(n))*floor(sqrt(n)).

Terms

a(0) =0a(1) =1a(2) =2a(3) =2a(4) =4a(5) =6a(6) =6a(7) =6a(8) =6a(9) =9a(10) =12a(11) =12a(12) =12a(13) =12a(14) =12a(15) =12a(16) =16a(17) =20a(18) =20a(19) =20a(20) =20a(21) =20a(22) =20a(23) =20a(24) =20a(25) =25a(26) =30a(27) =30a(28) =30a(29) =30