Documentation for Crowd 2.2. Documentation for other versions of Crowd is available too.
There are three ways to find your Support Entitlement Number (SEN).
Select 'Administration', 'License Details'. The SEN is shown:
Your Support Entitlement Number is available at http://my.atlassian.com:
Your Support Entitlement Number (SEN) appears on the third page of your Atlassian invoice.
See Finding Your Support Entitlement Number in the support space for more general information about how Atlassian Support uses this number.