In the rate of growth you're using, the numbers are not sustainable. I don't exactly understand your math, but I tried to use your population basis out to 50 years as a sample. I used years and each generation. By year 50 the population profile (adults are over 16, children under 16) would be:
Generation 1: 6 adults
Generation 2: 102 adults 18 children
Generation 3: 270 adults 690 children
Generation 4: 3 adults 987 children
Generation 5: 6 children
This gives you a population profile of about 381 adults to 1698 children. 4.5:1 ratio of kids to adults. So the agressive population approach you've used does have a steep increase; however, that population growth strongly favors the infants. At this point, granny of generation 1 is still dealing with her own 10 year-old 40th child, so don't expect her to help with your 16 kids between the ages of 16 to newborn. She spent her first 40 years popping out a baby every year, so she's already sick of looking at kids. Just imagine the first 8 adults (if we include Mr. and Mrs. Noah) living in the post-flood wasteland with 48 kids age 16 to infant. In a world of this kind of population growth, dad isn't going to have time to get together with the guys to build a tower.
That was why WT set a Towertime population of over 4,000 adult males.
I think I mentioned it earlier in this thread, but the bible doesn't really support aggressive population growth. Where families are named, only 4 or 5 sons are mentioned. Maybe there really were 20 sons for each instead of just the few? That's not what the bible says. It would have been easy to name the prominent ones and say "18 other sons". Instead, the bible sounds rather clear that it was naming them all. From the account, it sounds like Noah left the ark with some few remarks afterward about the few kids/grandkids. Then the story picks up shortly later with the world completely repopulated seemingly to pre-flood levels. Even the Nephilim are spoken of in Numbers. When you look at the example of Abraham and Isaac, fertility wasn't high. Jacob had a large brood... which was 12 sons... by 4 different women.
Sure, math can be used to propose a huge population. But it doesn't fit with the story. Similarly, as mentioned in this thread, the account of the Hebrew population growth in Egypt doesn't work. Conversely, in the story of Solomon's Temple, it goes to the other extreme. Where the Tower of Babel says nothing of the numbers involved and the math comes up small, the account of the temple uses astronomically large numbers for the amount of gold, number of cattle and sheep slaughtered, etc. Just evaluating the number of cattle compared to the small size of Jerusalem, and you realize... that's a lot of bull$h!t.
But I've gotten off-topic of my own thread. For more interesting analysis, read The Atheists Book of Bible Stories. If you don't have your copy, hopefully the link on this thread is working.
http://www.jehovahs-witness.net/watchtower/bible/154236/4/The-Atheists-Book-of-Bible-Stories#.U7CSG7HDuSo