Riordan numbers: a(n) = (n-1)*(2*a(n-1) + 3*a(n-2))/(n+1).

Terms

a(0) =1a(1) =0a(2) =1a(3) =1a(4) =3a(5) =6a(6) =15a(7) =36a(8) =91a(9) =232a(10) =603a(11) =1585a(12) =4213a(13) =11298a(14) =30537a(15) =83097a(16) =227475a(17) =625992a(18) =1730787a(19) =4805595a(20) =13393689a(21) =37458330a(22) =105089229a(23) =295673994a(24) =834086421a(25) =2358641376a(26) =6684761125a(27) =18985057351a(28) =54022715451a(29) =154000562758