a(n) = [ C(2n,n)/2^(n+2) ].

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =1a(6) =3a(7) =6a(8) =12a(9) =23a(10) =45a(11) =86a(12) =165a(13) =317a(14) =612a(15) =1183a(16) =2292a(17) =4451a(18) =8654a(19) =16853a(20) =32865a(21) =64165a(22) =125414a(23) =245375a(24) =480526a(25) =941832a(26) =1847440a(27) =3626457a(28) =7123398a(29) =14001162