The classic example here is Strassen's algorithm. You divide your two input matrices into quarters, and then you need to do 7 matrix multiplies of the smaller (

The classic example here is Strassen's algorithm. You divide your two input matrices into quarters, and then you need to do 7 matrix multiplies of the smaller (n/2) matrices. When you add up the total work done, this ends up needing to do n^(log base 2 of 7) work, or about n^2.8.