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

Terms

a(0) =1a(1) =2a(2) =1a(3) =6a(4) =4a(5) =1a(6) =18a(7) =16a(8) =6a(9) =1a(10) =54a(11) =60a(12) =30a(13) =8a(14) =1a(15) =162a(16) =216a(17) =134a(18) =48a(19) =10a(20) =1a(21) =486a(22) =756a(23) =558a(24) =248a(25) =70a(26) =12a(27) =1a(28) =1458a(29) =2592