Series Summation Problem $1+2+3+\dots+n=k$
75279
Reversing the $T(n) = \frac{n(n+1)}{2}$ formula
62271
Find the sum of the series: $\cos^3 \alpha +\cos^3 {3\alpha} + \cos^3 {5\alpha}+....+\cos^3 {(2n-1)\alpha}$.
110996
Sum of the form $r+r^2+r^4+\dots+r^{2^k} = \sum_{i=1}^k r^{2^i}$
69045
Solving this summation: $\sum_{i=1}^k i\cdot2^i$
102339
How to compute the sum of a series
11612
How to show that $\sum_{k=1}^n k(n+1-k)=\binom{n+2}3$?
33104
Combinatorial Proof with Summation Identity
83641
The sum of the series $\frac{15}{16}+\frac{15}{16} \times \frac{21}{24}+\frac{15}{16} \times \frac{21}{24} \times \frac{27}{32}+\dots$
146491
Number of solutions of $x_1+x_2+\dots+x_k=n$ with $x_i\le r$
134610
Find the sum of finite series $S=\sum_{k=1}^{2015}{(-1)^{\frac{k(k+1)}{2}}}k$
30518
Formula for $\sum_{k=1}^n \frac{1}{k(k+1)(k+2)}$?
17390
Find $LK_1^2 + LK_2^2 + \dots + LK_{11}^2$.
122534
Show that $\sum (-1)^{n+1}/n$ = $k$ can be expanded to a sum with $ 1 - 1/2 + 1/3 + 1/5 - 1/4 +1/7 + 1/9 - 1/6 + ....$ which is $3k/2$
57549
Finding the sum $\sum_{k=1}^rk^2\binom {n-k}{r-k}$
18814
Sum of the series $1+\frac{1\cdot 3}{6}+\frac{1\cdot3\cdot5}{6\cdot8}+\cdots$
150355
Finding sum of binomial series
134311
How to determine equation for $\sum_{k=1}^n k^3$