a(n) = floor((10*n^3 + 63*n^2 + 126*n + 89) / 72).

Terms

a(0) =1a(1) =4a(2) =9a(3) =18a(4) =31a(5) =49a(6) =73a(7) =104a(8) =142a(9) =189a(10) =245a(11) =311a(12) =388a(13) =477a(14) =578a(15) =693a(16) =822a(17) =966a(18) =1126a(19) =1303a(20) =1497a(21) =1710a(22) =1942a(23) =2194a(24) =2467a(25) =2762a(26) =3079a(27) =3420a(28) =3785a(29) =4175