So, I guess this is more of a Computer Science 101 question, but I figured it out.
for row in 1 2 3 4
for col in 1 2 3 4
index = ((row - 1) * 4) + col
li.item{index}
background-position (((row - 1) * 130 + ((row - 1) * 2)) * -1px) (((col - 1) * 130 + ((col - 1) * 2)) * -1px)