a(n) = ceiling(n^3*(Pi/2)).

Terms

a(0) =2a(1) =13a(2) =43a(3) =101a(4) =197a(5) =340a(6) =539a(7) =805a(8) =1146a(9) =1571a(10) =2091a(11) =2715a(12) =3452a(13) =4311a(14) =5302a(15) =6434a(16) =7718a(17) =9161a(18) =10775a(19) =12567a(20) =14548a(21) =16726a(22) =19112a(23) =21715a(24) =24544a(25) =27609a(26) =30918a(27) =34483a(28) =38311a(29) =42412