Simplifying $\sum_{k=1}^{n} \frac1{k(k+1)}$
14306
What is the formula for $\frac{1}{1\cdot 2}+\frac{1}{2\cdot 3}+\frac{1}{3\cdot 4}+\cdots +\frac{1}{n(n+1)}$
50606
Find $\sum\limits_{k\, \text{ odd}} \frac{2(k^2-1)}{k^4+k^2+1}$
140877
Evaluate the sum $\sum_{k=1}^n {n \choose k-1} {n \choose k}$
153226
Proof of $\sum_{k = 1}^{n} \frac{1}{k^{2}} < 2 - \frac{1}{n}$
35381
Sum with binomial coefficients: $\sum_{k=1}^m  \frac{1}{k}{m \choose k} $
43903
Find the sum for $\sum_{n=1}^{\infty}(-1)^{(n+1)}\frac{2n+1}{3^n} $
12423
"Closed" form for $\sum \frac{1}{n^n}$
20317
Proving $\sum_{k=1}^{n}{(-1)^{k+1} {{n}\choose{k}}\frac{1}{k}=H_n}$
29524
Formula for the sum $\sum_{i=2}^{n} \frac1{i^2-1}$
64581
How to find the sum $\sum\limits_{k=1}^n (k^2+k+1)k!$?
59252
Show $\sum_{k=0}^{m} \binom{n-k}{m-k}=\binom{n+1}{m}$
15932
How to simplify the summation kk! without using induction?
3798
Finding formula for sum $S_n = \sum_{i=1}^n i(i-1)$
146762
Closed form for $\sum_{k=0}^{n} \binom{n}{k}\frac{(-1)^k}{(k+1)^2}$
114414
Sum of $\sum_{k=1}^n\sin{k\theta}$
142985
Finding sum of series $\sum^{\infty}_{k=0}\frac{(k+1)(k+2)}{2^k}$
51679
Simplifying the product $\prod\limits_{k=2}^n \left(1-\frac1{k^2}\right)$