geometric sequence and the first generation, math homework

One of the many uses of sequences and series is to find out the population of a colony of insects generation after generation. Lets say, there was a colony of ants where their number ants  after the first generation is double the number in the previous generation. This kinda  sequence is geometric sequence.There is a common ratio of 2. If the first generation had 100 ants we can find the number of ants in the 5th generation by the formula an = a1r^n-1 where n is 5 and a1 is 100 and r is 2.

a5 = 100*2^5-1

a5= 100*2^4

a5 = 1600

– I need you to make an example similar to this