Riordan array (1, x(1 - 4x)/(1 - 7x + 3x^2)).

Terms

a(0) =1a(1) =0a(2) =1a(3) =0a(4) =3a(5) =1a(6) =0a(7) =18a(8) =6a(9) =1a(10) =0a(11) =117a(12) =45a(13) =9a(14) =1a(15) =0a(16) =765a(17) =342a(18) =81a(19) =12a(20) =1a(21) =0a(22) =5004a(23) =2556a(24) =702a(25) =126a(26) =15a(27) =1a(28) =0a(29) =32733