a(n) = n*(n+1)*(4*n+5)/6.

Terms

a(0) =0a(1) =3a(2) =13a(3) =34a(4) =70a(5) =125a(6) =203a(7) =308a(8) =444a(9) =615a(10) =825a(11) =1078a(12) =1378a(13) =1729a(14) =2135a(15) =2600a(16) =3128a(17) =3723a(18) =4389a(19) =5130a(20) =5950a(21) =6853a(22) =7843a(23) =8924a(24) =10100a(25) =11375a(26) =12753a(27) =14238a(28) =15834a(29) =17545