Who knows thirteen?
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. (What, you thought we'd stop here?)
13 are the midos of Yishmael.
(Obvious, but it fits the rhythm!)
13 are the "mechilin" in Aramaic to correspond to any 13 "midos" in Hebrew, which we usually translate as "measures." If exegetic techniques are considered "measures", that explains why the exegetic work on Exodus is called the Mechilta.
Thirteen are the shofaros* in the Beis Hamikdash (Mishnah, Shekalim 6:5).
* Money boxes, shaped like a shofar (narrow on top, wide on the bottom, to prevent theft of the contents). They were used for various kinds of contributions to the Beis Hamikdash and its operations.
Thirteen are the number of covenants associated with bris milah (Nedarim 31b).
Thirteen is the Gematria of Ehad, ...which leads us back to... Bas613's answer at Echad - mi yodeya? ! (Thank you Shalom! My short term memory is not doing too well these days!)
13 is the number of tribes which Eretz Israel will be divided in the future (Bava Basra 122a).
Thirteen is the number of young bulls that are offered on the alter on the 1st day Sukkot 13You shall offer up a burnt offering, a fire offering for a spirit of satisfaction to the Lord: thirteen young bulls, two rams, fourteen lambs in the first year; they shall [all] be unblemished.
במדבר כט י״ג אִשֵּׁ֨ה רֵ֤יחַ נִיחֹ֨חַ֙ לַֽיהֹוָ֔ה פָּרִ֧ים בְּנֵֽי־בָקָ֛ר שְׁלשָׁ֥ה עָשָׂ֖ר אֵילִ֣ם שְׁנָ֑יִם כְּבָשִׂ֧ים בְּנֵֽי־שָׁנָ֛ה אַרְבָּעָ֥ה עָשָׂ֖ר תְּמִימִ֥ם יִֽהְיֽוּ:
Thirteen were the number of towns that were allocated to the children of Gershon.
יהושע כ״א ו
וְלִבְנֵ֣י גֵרְשׁ֗וֹן מִמִּשְׁפְּח֣וֹת מַטֵּֽה־יִשָּׂשכָ֣ר וּמִמַּטֵּֽה־אָ֠שֵׁר וּמִמַּטֵּ֨ה נַפְתָּלִ֜י וּ֠מֵחֲצִי מַטֵּ֨ה מְנַשֶּׁ֤ה בַבָּשָׁן֙ בַּגּוֹרָ֔ל עָרִ֖ים שְׁלֹ֥שׁ עֶשְׂרֵֽה׃
To the Gershonites [there fell] by lot 13 towns from the clans of the tribe of Issachar, the tribe of Asher, the tribe of Naphtali, and the half-tribe of Manasseh in Bashan.