a(n) = floor(binomial(2*n,n)/3^n).

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =1a(7) =1a(8) =1a(9) =2a(10) =3a(11) =3a(12) =5a(13) =6a(14) =8a(15) =10a(16) =13a(17) =18a(18) =23a(19) =30a(20) =39a(21) =51a(22) =67a(23) =87a(24) =114a(25) =149a(26) =195a(27) =255a(28) =334a(29) =438