a(n) = (4n)! / ( 4^n * (2n)! ).A101485a(n) = (4n)! / ( 4^n * (2n)! ).Terms a(0) =1a(1) =3a(2) =105a(3) =10395a(4) =2027025a(5) =654729075a(6) =316234143225External referencesoeis: A101485