Number of DD's in all skew Dyck paths of semilength n.

Terms

a(0) =0a(1) =0a(2) =1a(3) =6a(4) =31a(5) =154a(6) =754a(7) =3670a(8) =17824a(9) =86524a(10) =420169a(11) =2041946a(12) =9932959a(13) =48368000a(14) =235769011a(15) =1150413818a(16) =5618786629a(17) =27468246832a(18) =134399280931a(19) =658139933938