a(n) = n^2*(n+1)*(2*n+1)/3.

Terms

a(0) =2a(1) =20a(2) =84a(3) =240a(4) =550a(5) =1092a(6) =1960a(7) =3264a(8) =5130a(9) =7700a(10) =11132a(11) =15600a(12) =21294a(13) =28420a(14) =37200a(15) =47872a(16) =60690a(17) =75924a(18) =93860a(19) =114800a(20) =139062a(21) =166980a(22) =198904a(23) =235200a(24) =276250a(25) =322452a(26) =374220a(27) =431984a(28) =496190a(29) =567300