First terms of first rows of zigzag matrices as defined in A088961.

Terms

a(0) =3a(1) =5a(2) =14a(3) =42a(4) =132a(5) =429a(6) =1430a(7) =4862a(8) =16796a(9) =58786a(10) =208012a(11) =742900a(12) =2674440a(13) =9694845a(14) =35357670a(15) =129644790a(16) =477638700a(17) =1767263190a(18) =6564120420a(19) =24466267020a(20) =91482563640a(21) =343059613650