Fourth-from-right diagonal of triangle A121207.

Terms

a(0) =1a(1) =1a(2) =5a(3) =20a(4) =85a(5) =400a(6) =2046a(7) =11226a(8) =65676a(9) =407787a(10) =2675410a(11) =18475311a(12) =133843405a(13) =1014271763a(14) =8019687099a(15) =66011609670a(16) =564494701167