Binomial coefficient C(5n,n-1).

Terms

a(0) =1a(1) =10a(2) =105a(3) =1140a(4) =12650a(5) =142506a(6) =1623160a(7) =18643560a(8) =215553195a(9) =2505433700a(10) =29248649430a(11) =342700125300