There are many prison numbers. Every prisoner had one. Here are some of the main characters':
Octavia Blake - Prisoner 167
John Murphy - Prisoner 285
Monty Green - Prisoner 308
Jasper Jordan - Prisoner 318
Clarke Griffin - Prisoner 319
Wells Jaha - Prisoner 325
Remember that Clarke is in solitary, meaning she had no roommate. I'm assuming Jasper and Monty had no roommate as well, due to all of their numbers beginning with 3, showing solitary. Also, Wells Jaha was probably the last Delinquent arrested because he got arrested the day they were sent down, so any number above his is unlikely.
If you would like the OC to be someones roommate, beside , Monty's, Clarke's, Jasper's, or Wells', here are some Prisoner Numbers for the others:
Octavia Blake - 166 or 168
John Murphy - 286
John Mbege - 211
Finn Collins - 221
Every other character is unaccounted for. Harper, Monroe, and Sterling were not in solitary for sure, because when they showed them boarding the dropship, it showed us that the Delinquents from solitary were boarded first. This means their number probably had 2 as the first number.
I don't know if this helped at all, or if it's even really important, but hey, I tried!
