Numbers 3:44-47

44Then the Lord spoke to Moses, saying,

45“Take the Levites [for Me] instead of all the firstborn among the sons of Israel, and the cattle of the Levites instead of their cattle. And the Levites shall be Mine. I am the Lord.

46For the ransom (redemption price) of the 273 of the firstborn of the Israelites who outnumber the Levites,

47you shall take five shekels apiece, per head, you shall take them in terms of the sanctuary shekel (the shekel is twenty gerahs),