Number of symmetric Catalan triangles of size n.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =12a(5) =36a(6) =168a(7) =768a(8) =5556a(9) =38904a(10) =435084a(11) =4676496a(12) =80726904a(13) =1333343808a(14) =35496821520a(15) =901465150464