a(n) = (2n+1)! / 2^n.A007019a(n) = (2n+1)! / 2^n.Terms a(0) =1a(1) =3a(2) =30a(3) =630a(4) =22680a(5) =1247400a(6) =97297200a(7) =10216206000External referencesoeis: A007019