Number of base pyramids in all skew Dyck paths of semilength n.

Terms

a(0) =0a(1) =1a(2) =3a(3) =9a(4) =30a(5) =109a(6) =420a(7) =1685a(8) =6960a(9) =29391a(10) =126291a(11) =550359a(12) =2426502a(13) =10803801a(14) =48507843a(15) =219377949a(16) =998436792a(17) =4569488371a(18) =21016589073a(19) =97090411019a(20) =450314942682