According to the NFL rules (Rule 5, Section 1, Article 4), wide receivers are only allowed to wear the following numbers: 10-19 or 80-89. Tight ends are only allowed to wear 80-89, so that limits the number of "80s" that can be used. When Evans arrived, the only numbers available to him were 12, 13, 17, 83. If 12 and 83 are "off-limits," that leaves unlucky 13 and number 17. I would have picked 83 if I were him, given the choices.
10 Greg Zolman
11 Drew Bledsoe
12 {Open}
13 {Open}
14 Kevin Beard
15 Jerel Myers
16 Cedric Bonner
17 {Open}
18 Drew Haddad
19 Jonathan Smith
80 Eric Moulds
81 Bobby Shaw
82 Josh Reed
83 {Open}
84 Mark Campbell
85 Clarence Coleman
86 Antonio Brown
87 Tim Euhus
88 Ryan Neufeld
89 Sam Aiken