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

Terms

a(0) =1a(1) =3a(2) =1a(3) =9a(4) =8a(5) =1a(6) =27a(7) =45a(8) =13a(9) =1a(10) =81a(11) =216a(12) =106a(13) =18a(14) =1a(15) =243a(16) =945a(17) =690a(18) =192a(19) =23a(20) =1a(21) =729a(22) =3888a(23) =3915a(24) =1574a(25) =303a(26) =28a(27) =1a(28) =2187a(29) =15309