How to calculate a special sum?
13098
Find a formula for $\sum\limits_{k=1}^n \lfloor \sqrt{k} \rfloor$
3798
Finding formula for sum $S_n = \sum_{i=1}^n i(i-1)$
86426
calculate $\sum_{1\le i\le r}\frac{i+1} { r+1}{2r-i\choose r-i}{s+i-2\choose i}+\frac{1}{r+1}{2r\choose r}$?
54661
How to find the sum $\sum\limits_{n=1}^{\infty}\frac{1}{n!(n^4+n^2+1)}$
64581
How to find the sum $\sum\limits_{k=1}^n (k^2+k+1)k!$?
130945
Summation using residues
50606
Find $\sum\limits_{k\, \text{ odd}} \frac{2(k^2-1)}{k^4+k^2+1}$
32866
How find this sum $\sum\limits_{n=0}^{\infty}\frac{1}{(3n+1)(3n+2)(3n+3)}$
52241
Calculate sum of series $\sum \frac{n^2}{n!}$
18461
Sum of odd Fibonacci Numbers
127806
How to find the sum of the series $\sum_{k=2}^\infty \frac{1}{k^2-1}$?
79814
Calculate sums of inverses of binomial coefficients
104078
Calculate the sum of the infinite series $\sum_{n=0}^{\infty} \frac{n}{4^n}$
142882
Can the factorial function be written as a sum?
18975
How to 'sum' a standard deviation?
157280
How do I sum up specific things in Numbers?
22657
How to find the sum of the infinite series?