Many Israelites joined, or sympathized with, Korah in his questioning of the authority of Moses, and they paid for it with their lives.
When Korah and those who joined him died by the hand of God, their sympathizers complained against Moses and Aaron, and God also punished those people, so that the Bible says,
“Now those who died in the plague were fourteen thousand seven hundred, besides those who died in the Korah incident” (Number 16.49).
It is interesting that fourteen thousand seven hundred died in the plague that followed, because fourteen thousand is a multiple of seven and so is seven hundred.
However, unless we can find something to indicate otherwise, this seems to be an incidental use of the number 7.