Numbers 3:40-43

The Numbers of the First-born Males in Israel above one Month. The figure (22,273) is out of proportion to the total population given in 146; for if it is doubled (for an equal number of females), the result is only 44,546, so that for every first-born person there were approximately 44 who were not first-born, which implies that the average family numbered 45. It has been sought to evade this conclusion by assuming that account is taken of only those first-born who were not themselves heads of families; but there is no hint of this restriction in the text.

Numbers 3:41. and the earth, etc. Since the firstlings of clean cattle could not be redeemed (Numbers 18:15; Numbers 18:17), read, and the cattle of the Levites instead of the cattle of all the first-born among the children of Israel.