Num 3:45-51

45Accept the Levites as substitutes for all the firstborn among the Israelites, and the livestock of the Levites as substitutes for their livestock; and the Levites shall be mine. I am the Lord.46As the price of redemption of the two hundred seventy-three of the firstborn of the Israelites, over and above the number of the Levites,47you shall accept five shekels apiece, reckoning by the shekel of the sanctuary, a shekel of twenty gerahs.48Give to Aaron and his sons the money by which the excess number of them is redeemed.49So Moses took the redemption money from those who were over and above those redeemed by the Levites;50from the firstborn of the Israelites he took the money, one thousand three hundred sixty-five shekels, reckoned by the shekel of the sanctuary;51and Moses gave the redemption money to Aaron and his sons, according to the word of the Lord, as the Lord had commanded Moses.