Echad Ve'esrim Ushlosh Meyot - mi yodeya?

Question

Who knows three hundred twenty-one?

?אחד ועשרים ושלוש מאות - מי יודע

In the spirit of the song "Echad - mi yodeya", please post interesting and significant Jewish facts about the number 321.

Answers that only contain lazy gematria may be avoided like fire.

Check out mi-yodeya-series for the previous three hundred twenty entries in this ongoing series.

Please include sources for your information wherever possible, as with all other answers on this site.

Answer 1

There are at most 321 days on which work is permitted per year, for those who live outside Israel. This occurs in a leap year starting on Shabbos, where Cheshvan and Kislev each have 30 days.

 385 days in the year
- 55 Shabbasos
- 13 days of Yom Tov
+  4 days of Yom Tov and Shabbos, which were double counted:
                                  Rosh Hashanah, Succos, Shemini Atzeres, and the 2nd day of Shavuos
----
 321 workdays

Answer 2

In the 321st year of the third millennium AM, Gad ben Ya'akov Avinu passed away at the age of 125.¹

In the 321st year of the fourth millennium AM, the prophet Yirmeyahu delivered the prophecy about the Destruction described in Yirmeyahu 25. In the same year, he dictated a cautionary written work (either a large part of his eponymous book or Eicha) only to have King Yehoyakim burn it up dismissively, as described in Yirmeyahu 36.²

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^{1. Seder Hadorot, Third Millennium, Year 321.}

^{2. Ibid., Fourth Millennium, Year 321.}