a(n) = (1/24)*n*(n + 5)*(n^2 + n + 6).

Terms

a(0) =2a(1) =7a(2) =18a(3) =39a(4) =75a(5) =132a(6) =217a(7) =338a(8) =504a(9) =725a(10) =1012a(11) =1377a(12) =1833a(13) =2394a(14) =3075a(15) =3892a(16) =4862a(17) =6003a(18) =7334a(19) =8875a(20) =10647a(21) =12672a(22) =14973a(23) =17574a(24) =20500a(25) =23777a(26) =27432a(27) =31493a(28) =35989a(29) =40950