Who knows seventeen?
Please cite/link your sources, if possible. After about one business day, I will:
Upvote all interesting answers.
Accept the best answer.
Go on to the next number.
Seventeen are the Yovel cycles.*
* From the conquest of Eretz Yisrael until the destruction of the first Beis Hamikdash. (Talmud, Erchin 12b) This was the only period in history when Yovel was binding.
Seventeen kohanim picked (on regular weekdays) to perform the daily services in the Beis Hamikdash (Rambam, Hil. Temidin Umussafin 4:5 ff).
Yosef was 17 when he was sold to Mitzrayim
Seventeen years lived Rabi (Rabi Yehudah HaNasi) in Tzipori.
Seventeen years lived Yaakov in Mitzrayim.
I'll start off with an easy one: gematria of Tov/טוב—good.
Bava Basra 10:1 Rabbi Yochanan ben Zakai dreamt on Rosh HaShana that his nephews will lose 700 gold coins that year. He kept on pushing them to give Tzedaka throughout the year. They were arrested towards the end of the year. He told them they are going to have to pay a fine of 17 gold coins.
17 is the reason that we don't eat nuts on Rosh Hashana! (חטא = 17 = אגוז without the alef - why we count חטא without the alef on Rosh Hashana is beyond the scope of this question)
Seventeen are the maximum number of mitzvos given to Benei Noach.