Number of stacked directed animals on the square lattice.

Terms

a(0) =1a(1) =2a(2) =6a(3) =19a(4) =63a(5) =213a(6) =729a(7) =2513a(8) =8703a(9) =30232a(10) =105236a(11) =366849a(12) =1280131a(13) =4470354a(14) =15619386a(15) =54595869a(16) =190891131a(17) =667590414a(18) =2335121082a(19) =8168950665a(20) =28580354769a(21) =100000811433a(22) =349918126509