n^3 + floor(n^3/2).

Terms

a(0) =1a(1) =12a(2) =40a(3) =96a(4) =187a(5) =324a(6) =514a(7) =768a(8) =1093a(9) =1500a(10) =1996a(11) =2592a(12) =3295a(13) =4116a(14) =5062a(15) =6144a(16) =7369a(17) =8748a(18) =10288a(19) =12000a(20) =13891a(21) =15972a(22) =18250a(23) =20736a(24) =23437a(25) =26364a(26) =29524a(27) =32928a(28) =36583a(29) =40500