Questions about generating specific levels

[Dibbla!]

Hi, I'm now using procgen and I cannot really figure how the following level is generated from current level. For example, I used the following code and I see the 'prev_level_seed is not following 0,1,2 sequence. Is there any parameter for this (I've tired use_sequential_levels=True and it doesn't work) ? Or I have to use num_levels with start_level for multiple times?

import gym
env = gym.make('procgen:procgen-coinrun-v0',start_level=0,num_levels=3)
print(env)
obs = env.reset()
total = 0
done_t=0

while True:
    obs, rew, done, info = env.step(0)
    total += rew
    if done:
        done_t += 1
        print(info,done_t)
        if done_t==100:
            break