So in our The Expanse ripoff Mars will be a very important player.
We've been thinking about colonization and population, and just how many people could be living on Mars 400 years in the future, lets call it 350 years after the first colonists.
Fortunately we have a perfectly good working model, the United States.
There was no one living here in 1607 when the first colonists arrived at James Town* and 1619 at Plymouth.
By 1700 250,000 people inhabited the 13 Colonies. By 1750 that population increased to 1.5 million. Over the course of one generation the population jumped to 2.5 million. In another generation it doubled to 5,000,000.
When the Civil War began there were 30 million Americans and at the turn of the century 75. That doubled again to 140 by World War II. When I was a kid in the 80's there were 230 million Americans, and now we've added another hundred million. So we've gone from 0 people in America** to 330 in just over 400 years.
So it is certainly possible that in 350 years there will be two hundred million Martians. That's a lot of people but still makes for a sparsely populated world. Which is kind of what we want.
**Also intentionally obtuse.