UCI BMX Permanent Career Number Applications
The UCI introduced on 1 August 2006 a permanent number system for Elite Men & Elite Women. With this system, riders can choose a “career number”, which they have the exclusive right to use for their entire Elite class career. This will give riders a possibility to market themselves and to give media and spectators an easy way to identify riders. Now for the eleventh time, Elite riders are given an opportunity to apply for number that is not yet in use.
Any riders who have a number that has expired (not scored any UCI points in the last season) will become vacant again. Such riders may re-apply for their number, although it will be subject to the normal procedure mentioned in the UCI rule book, § 10 International permanent race number system, (art. 6.1.073 to 6.1.076).
No later than 15 October 2016, each National Federation shall submit the attached application form that you can find here for all their Elite Men & Elite Women and Juniors Men and Women moving up to Elite in 2017 who wish to receive UCI BMX Permanent Career Number. That is, riders who were born in 1998 or earlier. Important: Applications received after 15 October will not be accepted.
Elite riders who finished in the top 8 at the 2016 UCI BMX World Championships can choose to race with their World Championships number 1 – 8 up until the next World Championships, or they may instead decide to continue using their existing permanent career number. In either case, this choice is definitive. Should they decide to use their world number 1–8 during this period, their career number will be reserved for them (art. 6.1.075). 
Important: If a rider believes that they might end the 2016 season without any points in the ranking of 31 December, 2016, they should re-apply for their career number to indicate to the UCI that they wish to keep using it.
You can find the list of 2016 UCI BMX available permanent career numbers here. 

http://www.uci.ch/newsletter/National_Federations_Newsletter/19_September/BMX_available-permanent-numbers.pdf