A transform of the little Schroeder numbers A001003.

Terms

a(0) =1a(1) =1a(2) =4a(3) =17a(4) =81a(5) =410a(6) =2169a(7) =11847a(8) =66306a(9) =378297a(10) =2192011a(11) =12864668a(12) =76313865a(13) =456837181a(14) =2756271064a(15) =16743326577a(16) =102319639173a(17) =628599899558