Numbers 3:45-48

“Take the Levites instead of all the firstborn among the sons of Israel and the cattle of the Levites. And the Levites shall be Mine; I am the LORD. For the ransom of the 273 of the firstborn of the sons of Israel who are in excess beyond the Levites, you shall take five shekels apiece, per head; you shall take them in terms of the shekel of the sanctuary (the shekel is twenty gerahs), and give the money, the ransom of those who are in excess among them, to Aaron and to his sons.”