Quadrinomial coefficients: C(2+n,n) + C(3+n,n) + C(4+n,n).

Terms

a(0) =3a(1) =12a(2) =31a(3) =65a(4) =120a(5) =203a(6) =322a(7) =486a(8) =705a(9) =990a(10) =1353a(11) =1807a(12) =2366a(13) =3045a(14) =3860a(15) =4828a(16) =5967a(17) =7296a(18) =8835a(19) =10605a(20) =12628a(21) =14927a(22) =17526a(23) =20450a(24) =23725a(25) =27378a(26) =31437a(27) =35931a(28) =40890a(29) =46345