Who knows nineteen?
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Nineteen are the years in a "machzor katan" - the cycle of regular and leap years in the Jewish calendar.
Nineteen are the Letters of R' Hirsch.
19 are the berachot in the 18
Nineteen are the books of Tanach that the Christians agree count as a single book each.
(Of the 24 books of the Tanach, Christians split each of Samuel, Kings, Chronicles, Ezra/Nechemiah, and Trei Asar into two or more books. That leaves nineteen. 5 of the Chumash + 5 Megilos + Yehoshua Shoftim Yishaya Yirmiya Yechzkel + Tehilim Mishlei Iyov + Daniel = 19. )
19 is the day of Kislev when R' Shneur Zalman of Liadi was released from prison.
19 were the years that Am Israel dwelled in Kadesh, and nineteen years they were wandering about aimlessly (see Rashi in Devarim 1:46)
Nineteen days is the longest possible tzara'at-quarantine. (Nega'im 3:8)