a(n) = 2*binomial(n,3).

Terms

a(0) =0a(1) =0a(2) =0a(3) =2a(4) =8a(5) =20a(6) =40a(7) =70a(8) =112a(9) =168a(10) =240a(11) =330a(12) =440a(13) =572a(14) =728a(15) =910a(16) =1120a(17) =1360a(18) =1632a(19) =1938a(20) =2280a(21) =2660a(22) =3080a(23) =3542a(24) =4048a(25) =4600a(26) =5200a(27) =5850a(28) =6552a(29) =7308