a(n) = n + n*(n-1)*(n-2)*(n-3)*(n-4)*(n-5).

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =4a(5) =5a(6) =726a(7) =5047a(8) =20168a(9) =60489a(10) =151210a(11) =332651a(12) =665292a(13) =1235533a(14) =2162174a(15) =3603615a(16) =5765776a(17) =8910737a(18) =13366098a(19) =19535059a(20) =27907220a(21) =39070101a(22) =53721382a(23) =72681863a(24) =96909144a(25) =127512025a(26) =165765626a(27) =213127227a(28) =271252828a(29) =342014429