Duplicate of A035508.

Terms

a(0) =0a(1) =2a(2) =7a(3) =20a(4) =54a(5) =143a(6) =376a(7) =986a(8) =2583a(9) =6764a(10) =17710a(11) =46367a(12) =121392a(13) =317810