Number of multi-directed animals on the square lattice.

Terms

a(0) =1a(1) =2a(2) =6a(3) =19a(4) =63a(5) =214a(6) =738a(7) =2571a(8) =9020a(9) =31806a(10) =112572a(11) =399548a(12) =1421145a(13) =5063254a(14) =18062902a(15) =64505148a(16) =230547424a(17) =824547052a(18) =2950565215a(19) =10562978104a(20) =37828967047a(21) =135516406962a(22) =485586082540