a(n) = n*(n - 1)*(n + 2)/2.

Terms

a(0) =0a(1) =4a(2) =15a(3) =36a(4) =70a(5) =120a(6) =189a(7) =280a(8) =396a(9) =540a(10) =715a(11) =924a(12) =1170a(13) =1456a(14) =1785a(15) =2160a(16) =2584a(17) =3060a(18) =3591a(19) =4180a(20) =4830a(21) =5544a(22) =6325a(23) =7176a(24) =8100a(25) =9100a(26) =10179a(27) =11340a(28) =12586a(29) =13920