50 points: Why is the number of cache lines always a power of 2? What is wrong with having 2049 or 2050 cache lines?

50 points: Suppose we have a 64KB direct-mapped cache with 2048 cache lines (each of 32-bytes) for 32-bit address system. Later we decide to use a 64KB 4-way set associative cache with only 1024 lines, each 16-bytes long. The tag field in the direct-mapped cache was 16 bits. (32 bits - 11 bits (to address into one of the 2048 lines) - 5 bits (to address into the 32 bytes.) How long will the tag field be in the new set associative cache?