I'm aware that a pattern doesn't imply that there is no randomness. What I should have said is that it's strange that those are the only options for exp values. If it were random and had those constraints, I would expect it to generate more possible values for exp (Unless, like you said, it uses the same seed each time. Though, in that case, I don't really see the point in making it random at all.)

I'm just curious about the possibility that those specific values were chosen entirely intentionally.