a(n) = Product_{k=1..n} (2k-1)!!.A057863a(n) = Product_{k=1..n} (2k-1)!!.Terms a(0) =1a(1) =1a(2) =3a(3) =45a(4) =4725a(5) =4465125a(6) =46414974375External referencesoeis: A057863