Why is the formula for the sum of infinite terms of a geometric progression only defined for $r < 1$?
101545
When is the formula for the infinite geometric series valid
58985
Does an increasing sequence of reals converge if the difference of consecutive terms approaches zero?
96961
A proof for the identity $\sum_{n=r}^{\infty} {n \choose r}^{-1} = \frac{r}{r-1}$
150092
Iterated sums and asymptotics
15305
How to understand intuitively the Stolz-Cesaro Theorem for sequences?
50230
Why does the order of summation of the terms of an infinite series influence its value?
75995
Infinite Sum - Result not correct for all cases?
42241
Evaluation of $\lim_{n\rightarrow \infty}\sum^{n}_{r=1}\frac{r}{n^2+n+r}$
25476
Question on geometrical proof of Geometric Series
129304
Alternative combinatorial proof for $\sum\limits_{r=0}^n\binom{n}{r}\binom{m+r}{n}=\sum\limits_{r=0}^n\binom{n}{r}\binom{m}{r}2^r$
69679
Geometric interpretation for sum of fourth powers
66272
Is there a common notion of $\mathbb{R}^n$, for non-integer $n$?
125981
Closed-Form Solution to Infinite Sum
34386
Sum of a complex, finite geometric series and its identity
107060
Confusion in proof for writing Poincares series in terms of Kloosterman sum
45892
arccot limit: $\sum_{r=1}^{\infty}\cot ^{-1}(r^2+\frac{3}{4})$
103572
Does $\sum_{m=1}^{\infty}\sum_{n=1}^{\infty}a_{mn}^3=\sum_{n=1}^{\infty}\sum_{m=1}^{\infty}a_{mn}^3$ occur here?