a(n) = (2n+2)!/(n!*2^(n+1)).

A001879

a(n) = (2n+2)!/(n!*2^(n+1)).

Terms

    a(0) =1a(1) =6a(2) =45a(3) =420a(4) =4725a(5) =62370a(6) =945945a(7) =16216200a(8) =310134825a(9) =6547290750a(10) =151242416325

External references