a(n) = Sum_{0<j<k<=n} k^3-j^3.

Terms

a(0) =7a(1) =52a(2) =208a(3) =608a(4) =1463a(5) =3080a(6) =5880a(7) =10416a(8) =17391a(9) =27676a(10) =42328a(11) =62608a(12) =89999a(13) =126224a(14) =173264a(15) =233376a(16) =309111a(17) =403332a(18) =519232a(19) =660352a(20) =830599a(21) =1034264a(22) =1276040a(23) =1561040a(24) =1894815a(25) =2283372a(26) =2733192a(27) =3251248a(28) =3845023a(29) =4522528