Largest divisor of n!/4 which is less than sqrt(n!)/2.

Terms

a(0) =2a(1) =5a(2) =12a(3) =35a(4) =96a(5) =288a(6) =945a(7) =3150a(8) =10800a(9) =39312a(10) =147420a(11) =571536a(12) =2286144a(13) =9424800a(14) =39984000a(15) =174283200a(16) =779688000a(17) =3573570000a(18) =16761064320a(19) =80379048750a(20) =393826406400