Number of modified skew Dyck paths of semilength n.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =20a(5) =73a(6) =281a(7) =1124a(8) =4627a(9) =19474a(10) =83421a(11) =362528a(12) =1594389a(13) =7083078a(14) =31738724a(15) =143281473a(16) =651048571a(17) =2975243348a(18) =13665866849a(19) =63055369522a(20) =292130900461