What is $\sum_{r=1}^n\frac{1}{r^2}$?
39659
Is there a closed formula for this summation?
42241
Evaluation of $\lim_{n\rightarrow \infty}\sum^{n}_{r=1}\frac{r}{n^2+n+r}$
57549
Finding the sum $\sum_{k=1}^rk^2\binom {n-k}{r-k}$
146533
Having problems proving $ \sum_{r=0}^{n}(r+1) \binom{n}{r} = (n+2)2^{n-1} $
37007
Evaluating $\sum_{k=1}^{n} \frac{1}{k(k+1)}$
138313
How to sum $\sum_{n=1}^{\infty} \frac{1}{n^2 + a^2}$?
114173
Explanation of the formulas for sums $\sum nr^n$ and $\sum n^2 r^n$
69084
What is the closed form for $\sum_{n=1}^\infty \frac1n - \frac1{n+1/p}$?
137640
Proof that $\sum_{1}^{\infty} \frac{1}{n^2} <2$
98808
Finite Sum $\sum_{i=1}^n\frac i {2^i}$
9587
If $f(t) = 1+ \frac{1}{2} +\frac{1}{3}+....+\frac{1}{t}$, find $\sum^n_{r=1} (2r+1)f(r)$ in terms of $f(n)$
17686
Evaluate the infinite series $\sum_{r=1}^{\infty} \frac{2^{-r}}{r^{2}}$
111705
Why does $\frac{1+t}{(1-t)^3}=\sum_{n=0}^{\infty}(1+n)^2t^n$
150148
Sum of $\sum^\infty_{n=2} \frac{1}{\ln{(n!)}}$
32637
What is the sum of this series: $\displaystyle\sum_{n=0}^{\infty} \dfrac{a^n}{(3n)!}$
139074
Question about $a_n=\sum_{k=1}^n \frac{n}{n^2+k}\ $for $ n \in\mathbb{N}$
141390
Closed form for $\sum_{n=-\infty}^\infty \frac{1}{(z+n)^2+a^2}$