Numbers 3:44-47

44Then the Lord said to Moses,

45‘Do not take the firstborn males among the people to belong to me. Accept the Levites instead. Do not use the firstborn animals of the people. Accept the animals of the Levites instead. The Levites will belong to me. I am the Lord.

46There are 273 more firstborn males of the people than there are Levites. So the people must pay for the extra firstborn sons.

47You must accept five shekels for each extra firstborn male. The shekel must have the same weight as the shekel that the Levites use in God's tabernacle. There are 20 gerahs in one shekel.