Greatest 4th power integer that divides n!

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =16a(6) =16a(7) =16a(8) =1296a(9) =20736a(10) =20736a(11) =20736a(12) =20736a(13) =20736a(14) =20736a(15) =331776a(16) =331776a(17) =429981696a(18) =429981696a(19) =268738560000a(20) =268738560000a(21) =268738560000a(22) =268738560000