What type of series is this: $k^n + k^{n-1} + k^{n-2} + k^{n-3}+\dots$

Question

I am wondering what type of series this this, where you have some constant (let's say 4) to the power of n, summed up where each new exponent keeps going $n-1, n-2, n-3, n-4, ...$ and so on. So,

$$4^{n} + 4^{n-1} + 4^{n-2} + 4^{n-3}+ ...$$

I thought it looked like a geometric series, but all I know about geometric series (I'm an amateur) would be something like this: $4^0 + 4^1 + 4^2 + 4^3 +...$

It looks like the number being subtracted from n is one less than the number of times you sum. I'm not sure how to express that mathematically, though!

Answer 1

$4^n * (1/4^0 + 1/4^1 + 1/4^2 … )$