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

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =1a(5) =2a(6) =7a(7) =6a(8) =9a(9) =1a(10) =3a(11) =12a(12) =19a(13) =36a(14) =27a(15) =27a(16) =1a(17) =4a(18) =18a(19) =40a(20) =91a(21) =120a(22) =162a(23) =108a(24) =81a(25) =1a(26) =5a(27) =25a(28) =70a(29) =185