Reference for Berakhot 7:3
כֵּיצַד מְזַמְּנִין, בִּשְׁלשָׁה אוֹמֵר נְבָרֵךְ. בִּשְׁלשָׁה וְהוּא, אוֹמֵר בָּרְכוּ. בַּעֲשָׂרָה, אוֹמֵר נְבָרֵךְ לֵאלֹהֵינוּ. בַּעֲשָׂרָה וָהוּא, אוֹמֵר בָּרְכוּ. אֶחָד עֲשָׂרָה וְאֶחָד עֲשָׂרָה רִבּוֹא. בְּמֵאָה אוֹמֵר, נְבָרֵךְ לַייָ אֱלֹהֵינוּ. בְּמֵאָה וְהוּא, אוֹמֵר בָּרְכוּ. בְּאֶלֶף, אוֹמֵר נְבָרֵךְ לַייָ אֱלֹהֵינוּ אֱלֹהֵי יִשְׂרָאֵל. בְּאֶלֶף וְהוּא, אוֹמֵר בָּרְכוּ. בְּרִבּוֹא, אוֹמֵר, נְבָרֵךְ לַייָ אֱלֹהֵינוּ אֱלֹהֵי יִשְׂרָאֵל אֱלֹהֵי הַצְּבָאוֹת יוֹשֵׁב הַכְּרוּבִים עַל הַמָּזוֹן שֶׁאָכָלְנוּ. בְּרִבּוֹא וְהוּא, אוֹמֵר בָּרְכוּ. כְּעִנְיָן שֶׁהוּא מְבָרֵךְ, כָּךְ עוֹנִין אַחֲרָיו, בָּרוּךְ יְיָ אֱלֹהֵינוּ אֱלֹהֵי יִשְׂרָאֵל אֱלֹהֵי הַצְּבָאוֹת יוֹשֵׁב הַכְּרוּבִים עַל הַמָּזוֹן שֶׁאָכָלְנוּ. רַבִּי יוֹסֵי הַגְּלִילִי אוֹמֵר, לְפִי רֹב הַקָּהָל הֵן מְבָרְכִין, שֶׁנֶּאֱמַר בְּמַקְהֵלוֹת בָּרְכוּ אֱלֹהִים, יְיָ מִמְּקוֹר יִשְׂרָאֵל (תהלים סח). אָמַר רַבִּי עֲקִיבָא, מַה מָּצִינוּ בְּבֵית הַכְּנֶסֶת, אֶחָד מְרֻבִּין וְאֶחָד מֻעָטִין אוֹמֵר, בָּרְכוּ אֶת יְיָ. רַבִּי יִשְׁמָעֵאל אוֹמֵר, בָּרְכוּ אֶת יְיָ הַמְבֹרָךְ:
How does one bless in a zimun? With three, he says: "Let us bless." With three and himself, he says: "Bless." [For there is a zimun without him; and thus with all.] With ten he says: "Let us bless our G-d." (And the same is true for) eleven and eleven myriads. [This first section is as per R. Akiva, who says that we do here (with zimun) as we do in the house of prayer. When the number reaches ten, it makes no difference whether there are many or few beyond that; here, too, there is no difference.] With a hundred, he says: "Let us bless the L-rd our G-d." [This second section is all as per R. Yossi Haglili, who says: "They bless according to the numerousness of the congregation, it being written (Psalms 68:27): 'In congregations bless G-d.'" And the halachah is that from three until, but not including, ten, the one reciting the blessing says: "Let us bless Him of whose fare we have eaten," and all respond: "Blessed be He of whose fare we have eaten and through whose good we live." From ten and above, the one reciting the blessing says: "Let us bless our G-d, of whose fare we have eaten," and all respond: "Blessed be our G-d, of whose fare we have eaten and through whose good we live."] With a hundred and himself he says: "Bless." With a thousand he says: "Let us bless the L-rd our G-d, the G-d of Israel." With a thousand and himself he says: "Bless." With ten thousand he says: "Let us bless the L-rd our G-d, the G-d of Israel, the G-d of hosts, the Dweller among the cherubs, for the fare that we have eaten." With ten thousand and himself he says: "Bless." In the manner that he blesses, so the others respond: "Blessed be the L-rd our G-d, the G-d of Israel, the G-d of hosts, the Dweller among the cherubs, for the fare that we have eaten." R. Yossi says: They bless according to the numerousness of the congregation, it being written (Psalms 68:7): 'In congregations bless G-d, the L-rd from the source of Israel.'" R. Akiva said: (We do with zimun) as we do in the house of prayer. Whether there are many or few, he says: "Bless the L-rd." R. Yishmael says: "Bless the L-rd, who is blessed." [And the halachah is in accordance with R. Yishmael.]