a(n) = 20*n^2.

Terms

a(0) =0a(1) =20a(2) =80a(3) =180a(4) =320a(5) =500a(6) =720a(7) =980a(8) =1280a(9) =1620a(10) =2000a(11) =2420a(12) =2880a(13) =3380a(14) =3920a(15) =4500a(16) =5120a(17) =5780a(18) =6480a(19) =7220a(20) =8000a(21) =8820a(22) =9680a(23) =10580a(24) =11520a(25) =12500a(26) =13520a(27) =14580a(28) =15680a(29) =16820