Denominator of n*Sum_{k=1..n} 1/(n+k).

Terms

a(0) =2a(1) =6a(2) =20a(3) =210a(4) =504a(5) =4620a(6) =51480a(7) =18018a(8) =272272a(9) =23279256a(10) =21162960a(11) =446185740a(12) =2059318800a(13) =5736673800a(14) =22181805360