a(n) = floor(C(2n,n)/2^n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =7a(6) =14a(7) =26a(8) =50a(9) =94a(10) =180a(11) =344a(12) =660a(13) =1269a(14) =2448a(15) =4733a(16) =9171a(17) =17804a(18) =34618a(19) =67415a(20) =131460a(21) =256661a(22) =501656a(23) =981501a(24) =1922106a(25) =3767329a(26) =7389761a(27) =14505829a(28) =28493592a(29) =56004648