For this task, add a collectible power up that has the effect of zapping all rocks with the same prime number as the "smart bomb".

To earn the collectible, there should occasionally be a small "bonus rock" of the matching prime.  This could be done various ways, but I would suggest that the existing prime number rocks occasionally acquire bonus status for a brief period (perhaps 1-2 seconds).  An alternative would to randomly do this when the rocks are spawned, but many of those get shot immediately, which would make it too easy.  The bonus rock should be drawn in some distinctive way, and have an accompanying sound.

The power-up itself should be activated by some key combination.  It should have the effect of zapping every rock on the screen that has the matching prime as a factor.  Additional visual or sound effects may be added at your discretion!