Apopulation of 400 beetles grows by 5% each week. how can the beetle population be determined after a number of weeks, w?

For this case we have an equation of the form:
 f (w) = A * (b) ^ w
 Where,
 A: initial amount
 b: growth rate
 w: number of weeks
 Substituting values we have:
 f (w) = 400 * (1.05) ^ w
 
 the beetle population can be determined after a number of weeks, w, with the following function:
 f (w) = 400 * (1.05) ^ w