Numbers 1:45-49

So all the numbered men of the sons of Israel by their fathers’ households, from twenty years old and upward, whoever was able to go to war in Israel,

all the numbered men were 603,550. Levites Exempted

The Levites, however, were not counted among them by their fathers’ tribe.

For the Lord had spoken to Moses, saying,

“Only the tribe of Levi you shall not count, nor shall you take their census among the sons of Israel.