How many repetitions does it take before there's an available domain name?

[simrob]

2 - zonezone.zone
2 - academyacademy.academy
2 - buildersbuilders.builders
3 - guruguruguru.guru
4 - bikebikebikebike.bike
5 - ususususus.us
5 - orgorgorgorgorg.org
6 - netnetnetnetnetnet.net
8 - comcomcomcomcomcomcomcom.com

2017 Update:
4 - zonezonezonezone.zone
3 - academyacademyacademy.academy
2 - buildersbuilders.builders
3 - guruguruguru.guru
4 - bikebikebikebike.bike
7 - ususususususus.us
6 - orgorgorgorgorgorg.org
∞ - all repeated .nets from 1-21 are taken!
21 - comcomcomcomcomcomcomcomcomcomcomcomcomcomcomcomcomcomcomcomcom.com

As of 2017, five-coms dot com is available through GoDaddy if you have a couple thousand dollars to spare, and two-academy dot academy is a premium domain available for $20.