Number of Dyck paths with n nodes and altitude 2.

Terms

a(0) =0a(1) =0a(2) =1a(3) =4a(4) =12a(5) =35a(6) =99a(7) =274a(8) =747a(9) =2015a(10) =5394a(11) =14359a(12) =38067a(13) =100610a(14) =265299a(15) =698359a(16) =1835922a(17) =4821695a(18) =12653739a(19) =33188674a(20) =87010587a(21) =228039695a(22) =597501714a(23) =1565251879a(24) =4099826787a(25) =10737374210a(26) =28118587299a(27) =73630970599a(28) =192799490322a(29) =504817832015