a(n) = (2*n-1)*(n^2 -n +6)/6.

Terms

a(0) =1a(1) =4a(2) =10a(3) =21a(4) =39a(5) =66a(6) =104a(7) =155a(8) =221a(9) =304a(10) =406a(11) =529a(12) =675a(13) =846a(14) =1044a(15) =1271a(16) =1529a(17) =1820a(18) =2146a(19) =2509a(20) =2911a(21) =3354a(22) =3840a(23) =4371a(24) =4949a(25) =5576a(26) =6254a(27) =6985a(28) =7771a(29) =8614