Certain directed lattice paths.

Terms

a(0) =1a(1) =6a(2) =33a(3) =189a(4) =1107a(5) =6588a(6) =39663a(7) =240894a(8) =1473147a(9) =9058554a(10) =55954395a(11) =346934745a(12) =2157989445a(13) =13459891500a(14) =84152389833a(15) =527224251861