Number of symmetrically unique Dyck paths of semilength n and height four.

Terms

a(0) =1a(1) =4a(2) =19a(3) =69a(4) =252a(5) =855a(6) =2867a(7) =9339a(8) =30085a(9) =95524a(10) =300796a(11) =939228a(12) =2915481a(13) =9001380a(14) =27675779a(15) =84782673a(16) =258956584a(17) =788926699a(18) =2398385803a(19) =7277878707a(20) =22050326805a(21) =66718218120a(22) =201640080056a(23) =608808949752