Staircase on Pascal's triangle.

Terms

a(0) =1a(1) =2a(2) =3a(3) =10a(4) =15a(5) =56a(6) =84a(7) =330a(8) =495a(9) =2002a(10) =3003a(11) =12376a(12) =18564a(13) =77520a(14) =116280a(15) =490314a(16) =735471a(17) =3124550a(18) =4686825a(19) =20030010a(20) =30045015a(21) =129024480a(22) =193536720a(23) =834451800a(24) =1251677700a(25) =5414950296a(26) =8122425444a(27) =35240152720a(28) =52860229080a(29) =229911617056