A symmetric triangle, with sum the large Schröder numbers.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =4a(5) =1a(6) =1a(7) =10a(8) =10a(9) =1a(10) =1a(11) =20a(12) =48a(13) =20a(14) =1a(15) =1a(16) =35a(17) =161a(18) =161a(19) =35a(20) =1a(21) =1a(22) =56a(23) =434a(24) =824a(25) =434a(26) =56a(27) =1a(28) =1a(29) =84