# Thread: Series sum question, is this correct?

1. ## Series sum question, is this correct?

Hi everyone

3. hi everyone,

sorry,the typo got missing.

question
Compute S5 for the following:
an(limit infinity, n=2) if an=(-1)^n +n^n

my working:

n=2,
-1^2 +2^2 = 5
n=3
-1^3+3^3=26
n=4
-1^4+4^4= 257
n=5
-1^5+5^5=3124
n=6
-1^6+6^6=46657
ans:5+26+257+3124+46657=50069

is it correct?thank you for helping

4. Originally Posted by anderson
hi everyone,

sorry,the typo got missing.

question
Compute S5 for the following:
an(limit infinity, n=2) if an=(-1)^n +n^n
What does "(lim infinity, n=2)" mean? If you are asking about the limit as n goes to infinity, it does not exist. This sequence does not converge.

my working:

n=2,
-1^2 +2^2 = 5
n=3
-1^3+3^3=26
n=4
-1^4+4^4= 257
n=5
-1^5+5^5=3124
n=6
-1^6+6^6=46657
ans:5+26+257+3124+46657=50069

is it correct?thank you for helping
Yes, those calculations are correct. And it should be easy now to see that the sequence is unbounded and does not converge to any finite limit.

5. thank you so much for guiding, i couldn't write it out with symbols cos there is no typo.
i guess i should have wrote limit=infinity, n=2.

am just wondering,is it possible to use the formula =n/2(2a+(n-1)d) to get the answer.i cant find the common ratio.need some opinion on this.

compute $S_5$ for $\sum_{n=1}^{infinity} a_n$ if
$a_n$= $(-1)^{n}$+ $n^{n}$