Partial products of A049820; a(1) = a(2) = 1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =6a(6) =30a(7) =120a(8) =720a(9) =4320a(10) =38880a(11) =233280a(12) =2566080a(13) =25660800a(14) =282268800a(15) =3104956800a(16) =46574352000a(17) =558892224000