a(n) = Sum_{0<=k<=n} ceiling(k^2/n).

Terms

a(0) =1a(1) =3a(2) =6a(3) =9a(4) =13a(5) =18a(6) =24a(7) =30a(8) =35a(9) =43a(10) =52a(11) =61a(12) =69a(13) =80a(14) =92a(15) =102a(16) =113a(17) =125a(18) =140a(19) =155a(20) =169a(21) =184a(22) =202a(23) =220a(24) =231a(25) =251a(26) =270a(27) =291a(28) =309a(29) =332