The Torah in Parashat Bamidbar tells of the process whereby the firstborns of Benei Yisrael were substituted by the tribe of Levi. As God explains to Moshe (3:12-13), the firstborns were consecrated on the night of the Exodus when He protected them from the plague that killed the Egyptian firstborns. He then later chose to replace the firstborns with the Leviyim. In order for this to happen, God commanded Moshe to count the Leviyim and then count all the firstborn in the nation. These censuses found that there were 273 more firstborns than Leviyim (3:46). God then instructed that as one Levi replaced one firstborn, the extra 273 firstborns needed to “redeem” themselves by paying a sum of five shekels. This money, God commanded, was to be given to Aharon and his sons (3:48).
Rav Meir Simcha Ha-kohen, in his Meshekh Chokhma, cites the Midrash (Bamidbar Rabba 4:10) as commenting that this money was divided into two equal portions, one of which was given to Aharon, and the other to his two sons (Elazar and Itamar). When God commanded giving the money to Aharon and his sons, He meant that half should go to Aharon, and the other half to his sons. Indeed (as Rav Meir Simcha cites earlier), there are also other contexts in which a command to give something “to Aharon and to his sons” requires dividing the item in question into two equal halves. In Masekhet Bava Batra (143a), for example, the Gemara comments that the lechem ha-panim – the special bread baked in the Beit Ha-mikdash – was to be divided into two equal portions, one of which went to the kohen gadol and the other to the other kohanim. Here, too, the Midrash explains that half of the firstborns’ redemption money was given to Aharon, and the other half to his sons.
Rav Meir Simcha adds that this method of distribution is consistent with the laws of pidyon ha-bein – the required “redemption” of a firstborn son – established by the Gemara in Masekhet Bekhorot (51b). The obligation of pidyon ha-bein requires giving five shekels to a kohen, but the Gemara establishes that one may fulfill the obligation by dividing this money among several different kohanim. Even though no single kohen receives the required amount, nevertheless, the mitzva is fulfilled since the required sum was given to kohanim. Rav Meir Simcha notes that this ruling can be proven from the redemption that took place in the wilderness, when the redemption money was divided into two equal halves. As precisely 273 firstborns were required to make this payment, it turns out that 272 of those payments were evenly divided between Aharon and his sons, but the 273rd then had to be split into two equal parts. The odd number of firstborns requiring redemption necessitated splitting one firstborn’s payment into two portions. This would seemingly prove that one fulfills his pidyon ha-bein obligation even if he divides the payment among two or more kohanim.
Interestingly, however, the Hafla’a (Rav Pinchas Horowitz), in his Panim Yafot commentary, disagrees with the Midrash’s reading. He writes that the redemption money specifically could not be divided into two equal portions, since each firstborn’s payment had to be given in full to a single recipient. According to the Panim Yafot, then, God required dividing this money evenly among Aharon, Elazar and Itamar. The number 273 is divisible by three, and thus each firstborn was able to make his payment in full to one of the three kohanim.
Several later writers questioned the Panim Yafot’s reading, noting that it seems to contradict both the Midrash and the Gemara’s aforementioned ruling in Masekhet Bekhorot. (See Rav Chaim Shaul Kaufman’s Mishchat Shemen, vol. 1, p. 314.)