Give me, please, first 10-15 answers.

It's not hard to get the correct formula for this problem, but harder to implement it because of high precision required.
At last I had to use precalculated array for getting AC.
Here's your answers:
2 -> 1.5
3 -> 2.25
4 -> 3.21428571
5 -> 4.48571429
6 -> 6.21981567
7 -> 8.64673579
8 -> 12.1044438
9 -> 17.0919353
10 -> 24.3495978

Ok, thank you!

What was the issue? For me straightforward implementation in C++ using double got AC easily.

How did you take 100th power of 3/2?
I can't think it out. I've never used decimal long arithmetic.

Edited by author 03.01.2013 16:06

Edited by author 03.01.2013 16:06

It is useful to remember that standard double type can store numbers up to 10^300 (and even a bit more). (3/2)^100 < 2^100 < 10^35
=> no problem to compute it in double. And since you need relative accuracy of only 7 digits => 16+ digits that double variable stores is more than enough to compute what you need.
Actually, here with usual double you can calculate answers for n up to 500+.

Is it really true?
I always thought that double type takes only 8 bytes of memory and hence cannot store such big numbers.
But anyway thank you. Maybe I just have bad compiler or bad implementation as always :)

RTFM =)
http://en.wikipedia.org/wiki/Double_precision

good test:
n=40 ans=3688328.070956036

The problem asks for at least 6 correct decimals. I had to compute up to 100 decimals (in intermediate computations) to get the required precision in the final answer for n = 100.

Here is the (censored) answer for the biggest possible test:
n = 100
answer = 13552*3*4*4*1*6*18.186159417