The total number of the firstborn males a month old or more, listed by name, was 22,273.
Here is the exchange made of the Levites for the first-born. 1. The first-born were numbered from a month old, Num 3:42, Num 3:43. Those certainly were not reckoned who, though first-born, had become heads of families themselves, but those only that were under age; and the learned bishop Patrick is decidedly of opinion that none were numbered but those only that were born since...
Commenting on Numbers 3:40-51
And the Lord spake unto Moses,.... After the number was taken, and gave him directions what to do upon it: saying; as follows.
Num 3:40-48 After this, Moses numbered the first-born of the children of Israel, to exchange them for the Levites according to the command of God, which is repeated in Num 3:41 and Num 3:44-45 from Num 3:11-13, and to adopt the latter in their stead for the service at the sanctuary (on Num 3:41 and Num 3:45, cf. Num 3:11-13).
Commenting on Numbers 3:40-48