a(n) = 20*(3*n)!/((2*n)!*(n+2)!).

Terms

a(0) =10a(1) =10a(2) =25a(3) =84a(4) =330a(5) =1430a(6) =6630a(7) =32300a(8) =163438a(9) =852150a(10) =4552275a(11) =24812400a(12) =137547000a(13) =773564328a(14) =4405019090a(15) =25357898940a(16) =147375745990a(17) =863805209750