Couldn't you get from a common ancestor to chimps & man
with 1667/2 (if 1667 is an ok number ... dunno where it
came from but hey ...)?
If the 1667 were split in half (I know, I know it's odd),
but where in different locations in the two lines,
you'd end up with 1667 differences.
So from a common (and different genetically) ancestor, you would
have to split the 1667 amongst the two lines.
Or however many mutations were actually accumulated.