If your civilization expands at a cubic rate through the universe, you can have one factor of linear growth for population (each couple of 2 has exactly 2 children when they're 20, then stop reproducing) and one factor of quadratic growth for minds (your mind can go as size N squared with time N). This can continue until the accelerating expansion of the universe places any other galaxies beyond our reach, at which point some unimaginably huge superintelligent minds will, billions of years later, have to face some unpleasant problems, assuming physics-as-we-know-it cannot be dodged, worked around, or exploited.

Meanwhile, PARTY ON THE OTHER SIDE OF THE MILKY WAY! WOO!