Hello math newbie here. Sorry need to ask this basic question.

What is the answer of

log (base 2) (100000 + 1) - 1

According to my info for log base 2 we divide it by log base 10 (2) for example

5 = log base 2 (32)

Now calculating log base 2 (32)

log base 2 (x) = log base 10 (x) / log base 10 (2)

So

log base 2 (32) = log base 10 (32) / log base 10 (2)

= 5

Now according to the above rule my answer comes out 15.60 i.e,

log (base 2) (100000 + 1) - 1

= log (base 2) (100001)-1

= 16.60 -1 = 15.60

but in my text book this is equal to 20.

Please tell what mistake I am doing?

Thank You!