Triangle read by rows, arising in study of alternating-sign matrices.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =5a(5) =2a(6) =9a(7) =36a(8) =36a(9) =9a(10) =90a(11) =495a(12) =855a(13) =495a(14) =90a(15) =2025a(16) =14175a(17) =34830a(18) =34830a(19) =14175a(20) =2025a(21) =102060a(22) =867510a(23) =2776032a(24) =4082400a(25) =2776032a(26) =867510a(27) =102060