[9^(4n+2)-9^(4n+1)]/81^(2n-1)
=[9*9^(4n+1)-9^(4n+1)]/9^(4n-2)
=[8*9^(4n+1)]/9^(4n-2)
=[8*9^(+1)]/9^(-2)
=8*9^3
=5832