Riordan array (1/((1-x)(1-3x)),x/((1-x)(1-3x))).

Terms

a(0) =1a(1) =4a(2) =1a(3) =13a(4) =8a(5) =1a(6) =40a(7) =42a(8) =12a(9) =1a(10) =121a(11) =184a(12) =87a(13) =16a(14) =1a(15) =364a(16) =731a(17) =496a(18) =148a(19) =20a(20) =1a(21) =1093a(22) =2736a(23) =2454a(24) =1040a(25) =225a(26) =24a(27) =1a(28) =3280a(29) =9844