Catalan's triangle with right border removed (n > 0, 0 <= k < n).

Terms

a(0) =1a(1) =1a(2) =2a(3) =1a(4) =3a(5) =5a(6) =1a(7) =4a(8) =9a(9) =14a(10) =1a(11) =5a(12) =14a(13) =28a(14) =42a(15) =1a(16) =6a(17) =20a(18) =48a(19) =90a(20) =132a(21) =1a(22) =7a(23) =27a(24) =75a(25) =165a(26) =297a(27) =429a(28) =1a(29) =8