Powers of 5

Hi, I'm an undergrad studying computer science. I discovered, while
studying for a computer science final, that I still haven't come up
with an answer to a question that was offered as extra credit on our
first quiz in the course. We were given the following Pascal code.

function power(n: integer): integer;
begin
if n <= 1 then
return (5)
else
return (5 * power(n-1))
end; {power}

We were then asked: "Can you modify the function in such a way that for
arguments of the form 2^k it computes the result with just k+1 calls?"
I'm not especially adept with math, and I have no idea how to approach
the question. Please point me in the right direction; I would really
like to understand this.

--
Josh Zenker

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