Triangle of numbers arising in enumeration of walks on square lattice.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =2a(5) =1a(6) =6a(7) =8a(8) =3a(9) =1a(10) =20a(11) =20a(12) =15a(13) =4a(14) =1a(15) =50a(16) =75a(17) =45a(18) =24a(19) =5a(20) =1a(21) =175a(22) =210a(23) =189a(24) =84a(25) =35a(26) =6a(27) =1a(28) =490a(29) =784