Leviticus 27:26-27 - Redemption Of The Firstborn
26 "No person is to consecrate the firstborn, because the firstborn of the animals already belongs to the LORD. Whether ox or goat, it belongs to the LORD. 27 If it's an unclean animal, then he is to ransom it according to your valuation, adding a fifth to it. If it's not redeemed, then it is to be sold according to your valuation.
40 Later the LORD instructed Moses: "Number all the first-born males of Israel from a month old and above and list their names. 41 Separate the descendants of Levi for me since I am the LORD in place of all the first-born sons of Israel. Also separate the livestock of the descendants of Levi in place of all the firstborn of the livestock of Israel." 42 So Moses numbered all the firstborn from the sons of Israel just as the LORD commanded him. 43 All the first-born males according to the list of their names from a month old and above numbered 22,273.
44 Then the LORD told Moses, 45 "Separate the descendants of Levi in place of all the firstborn sons of Israel and the livestock of the descendants of Levi in place of their livestock. The descendants of Levi belong to me, since I am the LORD.
46 You are to pay a ransom for the 273 first-born Israelis who exceed the census number of the descendants of Levi, 47 so collect five shekels for each individual, denominated in shekels of the sanctuary, that is, the shekel that weighs 20 gerahs. 48 Then give the money meant for ransom of their excess to Aaron and his sons."
49 So Moses took the ransom money to account for the difference in the total number of those redeemed by the descendants of Levi. 50 From the firstborn of the Israelis, Moses took money amounting to 1,365 shekels according to the shekel of the sanctuary. 51 Moses gave the ransom money to Aaron and his sons according to the LORD's instructions, just as the LORD had commanded Moses.