Way to select area with coords?

I'm making a block and I wanna make it so that when a Mob is close to it, it will spawn a powerful mob. I can't make it detect mobs so I thought maybe I could have the mobs detect the block using mob tick update and stuff. Is there a way to select a large area of blocks without needing to point out each individual block? Something like:

Numbers:1-5 + Entity X Coord