a creature has a fertile period for 800 years and has one child a year totaling 800 children over the life span

Question

Here is the question
Let’s assume a creature has a fertile period for 800 years and has one child a year totaling 800 children over the life span
Each offspring is able to breed at 20 years of age. Having one child per year.
Assume equal amounts of males and females was produced by the original female and all ofspring after

Each pair continues to have offspring after ageing at least 20 years as does their offspring so on and so on
All equations stop at the original female’s point of death at 800 years. Assuming equal male and female always produced, with single births, no twins each 12 months after age of 20 years, with each new female continuing to have an offspring every 12 months. No fatalities during this 800 year span.
How many total offspring’s are able to be produced during the 800 years through each generation?

Answer 1

 

roughly 2.62... x 10^1013

 

800  * 390^390

 

becuase 800 - 20 = 780.

Half of 780 is 390