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

Terms

a(0) =0a(1) =0a(2) =2a(3) =7a(4) =16a(5) =30a(6) =50a(7) =77a(8) =112a(9) =156a(10) =210a(11) =275a(12) =352a(13) =442a(14) =546a(15) =665a(16) =800a(17) =952a(18) =1122a(19) =1311a(20) =1520a(21) =1750a(22) =2002a(23) =2277a(24) =2576a(25) =2900a(26) =3250a(27) =3627a(28) =4032a(29) =4466