Riordan array (1/sqrt(1-2*x-3*x^2), (1-2*x-3*x^2)/(2*(1-3*x)) - sqrt(1-2*x-3*x^2)/2).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =2a(5) =1a(6) =7a(7) =5a(8) =3a(9) =1a(10) =19a(11) =13a(12) =8a(13) =4a(14) =1a(15) =51a(16) =35a(17) =22a(18) =12a(19) =5a(20) =1a(21) =141a(22) =96a(23) =61a(24) =35a(25) =17a(26) =6a(27) =1a(28) =393a(29) =267