Triangle, read by rows, where the n-th row lists the (2n+1) coefficients of (1+2*x+3*x^2)^n.

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =1a(5) =4a(6) =10a(7) =12a(8) =9a(9) =1a(10) =6a(11) =21a(12) =44a(13) =63a(14) =54a(15) =27a(16) =1a(17) =8a(18) =36a(19) =104a(20) =214a(21) =312a(22) =324a(23) =216a(24) =81a(25) =1a(26) =10a(27) =55a(28) =200a(29) =530