Who knows fifty-three?
Please cite/link your sources, if possible. At some point in the next few days, I will:
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Accept the best answer.
Go on to the next number.
53 is the maximum number of consecutive days with something "extra" in the evening prayers. And it happens twice. At least on this year's calendar, outside of Israel.
In the late summer / early fall: The night going into the 30th of Av gets Yaaleh v'yavo; the 29 nights of Elul all get L'David Hashem Ori V'Yishi (Psalm 27). The 22 nights of Tishrei through Shmini Atzeres get Psalm 27 as well. And the night concluding Shmini Atzeres gets "ata hareisa" and Simchas Torah. That makes 53.
On this year's calendar, the night concluding Simchas Torah gets no "ata chonantanu", as it's a Friday night. Just the usual, unmodified, Friday-night prayers.
In the spring / early summer: The night going into the 15th of Nisan is a holiday and has ya'aleh v'yavo; the next 49 nights have Sefiras HaOmer. The next two nights are holiday, and the next night concludes with "ata chonantanu." 53.
53 are the chapters in each of two consecutive books of the Rambam's Mishneh Torah: Nashim and Kedushah.
"Parashas mishpatim has in it 23 do mitzvos and 30 don't do." Head note to Sefer Hachinuch, Parashas Mishpatim