a(n) = (35*n^4 - 35*n^3 + 55*n^2 - 25*n + 6)/6.

Terms

a(0) =6a(1) =76a(2) =386a(3) =1251a(4) =3126a(5) =6606a(6) =12426a(7) =21461a(8) =34726a(9) =53376a(10) =78706a(11) =112151a(12) =155286a(13) =209826a(14) =277626a(15) =360681a(16) =461126a(17) =581236a(18) =723426a(19) =890251a(20) =1084406a(21) =1308726a(22) =1566186a(23) =1859901a(24) =2193126a(25) =2569256a(26) =2991826a(27) =3464511a(28) =3991126a(29) =4575626