A closed expression for $\sum_{k=1}^n\cos(kA)$
5080
How can we sum up $\sin$ and $\cos$ series when the angles are in arithmetic progression?
14197
show that $\sum_{i=0}^l \dfrac{{l\choose i}}{{n\choose k + i}} = \dfrac{n+1}{(n-l+1) {n-l\choose k}}$
107789
Sum of $\sum \limits_{n=0}^{\infty} \frac{1}{(kn)!}$
91933
Evaluate $\sum_{k=1}^nk\cdot k!$
110569
Does anyone know a closed-form expression for a bijection between $\mathbb{N}^k$ and $\mathbb{N}$?
86497
Prove that any rational can be expressed in the form $\sum\limits_{k=1}^n{\frac{1}{a_k}}$, $a_k\in\mathbb N^*$
110441
Closed form for a formula with a summation over $i\binom{n-i}{k-1}$, and combinatorial proof?
110262
Finding a closed formula for $1\cdot2\cdot3\cdots k +\dots + n(n+1)(n+2)\cdots(k+n-1)$
21000
Calculating $\sum_{k=1}^nk(k!)$ combinatorially
136652
Closed form expression for the product $\prod\limits_{k=1}^{n}\left(1 - \frac{1}{ak}\right)$
118024
Simplify the expression $\binom{n}{0}+\binom{n+1}{1}+\binom{n+2}{2}+\cdots +\binom{n+k}{k}$
125981
Closed-Form Solution to Infinite Sum
47670
Algebraic proof of $\sum_{i=0}^k{{n \choose i}{m \choose {k-i}}}= {{m+n}\choose k}$
124229
Simplify $\sum_{k=0}^{\infty} x^ky^{\frac{k(k+1)}{2}}$
37007
Evaluating $\sum_{k=1}^{n} \frac{1}{k(k+1)}$
121617
Closed form of $\sum_{n=0}^{\infty} \frac{\cos(\alpha \, n)}{n!}$
119606
Closed form of summation