675.

The next number in the sequence is n squared minus m or f(n,m) = n² – m
f(6,9) = 6² – 9 = 27
f(9,27) = 9² – 27 = 54
f(27,54) = 27² – 54 = 675
f(54,675) = 54² – 675 = 2241