Triangular array, read by rows: first differences in n,n direction of trinomial array A027907.

Terms

a(0) =1a(1) =1a(2) =0a(3) =1a(4) =1a(5) =1a(6) =2a(7) =1a(8) =1a(9) =1a(10) =2a(11) =4a(12) =4a(13) =4a(14) =2a(15) =1a(16) =1a(17) =3a(18) =7a(19) =10a(20) =12a(21) =10a(22) =7a(23) =3a(24) =1a(25) =1a(26) =4a(27) =11a(28) =20a(29) =29