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69
The sum of irrationals is irrational?
math.stackexchange.com

56
Was mathematics invented or discovered?
philosophy.stackexchange.com

36
Crazy induction
math.stackexchange.com

35
Logic question: Ant walking a cube
math.stackexchange.com

32
Find all roots of $\,(x + 1)(x + 2)(x + 3)^2(x + 4)(x + 5) = 360$
math.stackexchange.com

31
Large integer help
math.stackexchange.com

30
Can you provide me historical examples of pure mathematics becoming “useful”?
math.stackexchange.com

29
Open math problems which high school students can understand
math.stackexchange.com

27
Finding $\int_0^{\pi/2} \sin x\,dx$
math.stackexchange.com

27
Proving an alternating Euler sum: $\sum_{k=1}^{\infty} \frac{(-1)^{k+1} H_k}{k} = \frac{1}{2} \zeta(2) - \frac{1}{2} \log^2 2$
math.stackexchange.com

26
Intuitive explanation of a positive-semidefinite matrix
math.stackexchange.com

26
How come the number $N!$ can terminate in exactly $1,2,3,4,$ or $6$ zeroes but never $5$ zeroes?
math.stackexchange.com

25
What's the formula of this sequence?
math.stackexchange.com

25
Is there a number that's right in the middle of this interval $(0, 1)$?
math.stackexchange.com

25
How to evaluate the series $1+\frac34+\frac{3\cdot5}{4\cdot8}+\frac{3\cdot5\cdot7}{4\cdot8\cdot12}+\cdots$
math.stackexchange.com

24
Determine $\lim_{x \to 0}{\frac{x-\sin{x}}{x^3}}=\frac{1}{6}$, without L'Hospital or Taylor
math.stackexchange.com

24
Why is every answer of $5^k - 2^k$ divisible by 3?
math.stackexchange.com

23
Is $\lim\limits_{k\to\infty}\sum\limits_{n=k+1}^{2k}{\frac{1}{n}} = 0$?
math.stackexchange.com

22
What was the first bit of mathematics that made you realize that math is beautiful? (For children's book)
math.stackexchange.com

21
Does the formula $\sqrt{ 1 + 24n }$ always yield prime?
math.stackexchange.com

21
Can you explain this card trick?
math.stackexchange.com

21
Show $\lim\limits_{n\to\infty} n \ln\left(1-\frac{1}n\right) = -1$
math.stackexchange.com

19
Value of $\sum_{n=0}^\infty (-1)^n$
math.stackexchange.com

18
evaluate the last digit of $7^{7^{7^{7^{7}}}}$
math.stackexchange.com

18
Find all positive integers $L$, $M$, $N$ such that $L^2 + M^2 = \sqrt{ N^2 +21}$
math.stackexchange.com

18
How to do integral $\int_{-\infty}^{\infty} x^4 e^{-x^2/2}dx$
math.stackexchange.com

17
$\lim_{n\to\infty} \left(\frac{1^p+2^p+3^p + \cdots + n^p}{n^p} - \frac{n}{p+1}\right)$ Evaluating this limit
math.stackexchange.com

17
An example of a norm which can't be generated by an inner product
math.stackexchange.com

16
If there are 200 students in the library, how many ways are there for them to be split among the floors of the library if there are 6 floors?
math.stackexchange.com

16
Importance of rank of a matrix
math.stackexchange.com

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