User Cocopuffs

32 votes

Accepted

How did Ramanujan get this result?

answered Jun 20, 2012 at 13:21

30 votes

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Prove that every number ending in a $3$ has a multiple which consists only of ones.

answered Jun 27, 2012 at 14:17

30 votes

Accepted

Prove that $2^n < \binom{2n}{n} < 2^{2n}$

answered Jul 21, 2013 at 16:07

26 votes

"Negative" versus "Minus"

answered Jun 11, 2012 at 21:51

22 votes

Prove that $ U(n^2−1)$ is not cyclic

answered Aug 14, 2012 at 16:30

18 votes

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Is it assumable that $2^{1/12}$ is irrational because $2^{1/2}$ is?

answered Jun 24, 2012 at 17:39

15 votes

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Non-Decreasing Digits

answered Jun 16, 2012 at 20:47

15 votes

Accepted

Simple number theory problem

answered Jun 3, 2013 at 20:24

15 votes

Finite set of zero-divisors implies finite ring

answered Jun 26, 2013 at 18:10

15 votes

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Find coefficient of $x^{100}$ in the power series expansion of $\frac{1}{(1-x)(1-2x)(1-3x)}$

answered Jul 6, 2013 at 8:16

15 votes

Accepted

Prove limit of $\frac1{n+1}+\frac1{n+2}+\ldots+\frac1{n+n}$ exists and lies between $0$ and $1$.

answered Sep 19, 2013 at 0:21

14 votes

Why $y^2-x^3-x^2$ is irreducible?

answered Sep 28, 2013 at 23:00

14 votes

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Eigenvalues and determinant of conjugate, transpose and hermitian of a complex matrix.

answered Oct 29, 2012 at 14:18

13 votes

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How do we know that $|i!| = \sqrt{\pi \operatorname{csch} \pi}$?

answered Jul 6, 2013 at 6:04

12 votes

Proving irreducibility of $x^6-72$

answered Jul 27, 2013 at 8:11

12 votes

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Computing $ \sum_{m=0}^{\infty} \sum_{n=0}^{\infty}\frac{1}{\Gamma \left(\frac{m+n}{2}\right)\Gamma \left(\frac{1+m+n}{2} \right)}$

answered Nov 20, 2012 at 21:44

11 votes

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proving that a number is a perfect square

answered Nov 18, 2012 at 15:09

11 votes

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infinite number of irreducible polynomials in $\mathbb{Z}/2{\mathbb Z}[X]$

answered Jul 3, 2012 at 13:18

10 votes

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Not divisible by $2,3$ or $5$ but divisible by $7$

answered Jul 24, 2013 at 19:24

9 votes

How do I solve this problem?

answered Jun 14, 2012 at 16:42

9 votes

Accepted

Tricky proof for a simple statement

answered Sep 17, 2012 at 13:16

9 votes

Value of $P(12)+P(-8)$ if $P(x)=x^{4}+ax^{3}+bx^{2}+cx+d$, $P(1)=10$, $P(2)=20$, $P(3)=30$

answered Jul 18, 2012 at 12:05

9 votes

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Prove $\sum_{i=1}^n$$w_i^2\geq\frac{1}{n}$ given $\sum_{i=1}^n w_i=1$

answered Jan 31, 2013 at 22:31

9 votes

How to derive a closed form of a simple recursion?

answered Apr 9, 2013 at 14:53

8 votes

Proving $\sqrt{2}\in\mathbb{Q_7}$?

answered Apr 13, 2013 at 11:17

8 votes

Accepted

Complex number with z to the power of 4

answered Aug 14, 2013 at 17:50

7 votes

How to prove $G_2$ is a normal subgroup of $G_1\times G_2$?

answered May 26, 2013 at 13:59

7 votes

Big List of Fun Math Books

answered Jul 7, 2012 at 22:53

7 votes

Accepted

Chain rule and inverse in matrix calculus

answered Jun 18, 2012 at 17:53

7 votes

Accepted

Flipping Cards Probability

answered Jun 16, 2012 at 19:33

Stack Exchange Network

173 Answers

How did Ramanujan get this result?

Prove that every number ending in a $3$ has a multiple which consists only of ones.

Prove that $2^n < \binom{2n}{n} < 2^{2n}$

"Negative" versus "Minus"

Prove that $ U(n^2−1)$ is not cyclic

Is it assumable that $2^{1/12}$ is irrational because $2^{1/2}$ is?

Non-Decreasing Digits

Simple number theory problem

Finite set of zero-divisors implies finite ring

Find coefficient of $x^{100}$ in the power series expansion of $\frac{1}{(1-x)(1-2x)(1-3x)}$

Prove limit of $\frac1{n+1}+\frac1{n+2}+\ldots+\frac1{n+n}$ exists and lies between $0$ and $1$.

Why $y^2-x^3-x^2$ is irreducible?

Eigenvalues and determinant of conjugate, transpose and hermitian of a complex matrix.

How do we know that $|i!| = \sqrt{\pi \operatorname{csch} \pi}$?

Proving irreducibility of $x^6-72$

Computing $ \sum_{m=0}^{\infty} \sum_{n=0}^{\infty}\frac{1}{\Gamma \left(\frac{m+n}{2}\right)\Gamma \left(\frac{1+m+n}{2} \right)}$

proving that a number is a perfect square

infinite number of irreducible polynomials in $\mathbb{Z}/2{\mathbb Z}[X]$

Not divisible by $2,3$ or $5$ but divisible by $7$

How do I solve this problem?

Tricky proof for a simple statement

Value of $P(12)+P(-8)$ if $P(x)=x^{4}+ax^{3}+bx^{2}+cx+d$, $P(1)=10$, $P(2)=20$, $P(3)=30$

Prove $\sum_{i=1}^n$$w_i^2\geq\frac{1}{n}$ given $\sum_{i=1}^n w_i=1$

How to derive a closed form of a simple recursion?

Proving $\sqrt{2}\in\mathbb{Q_7}$?

Complex number with z to the power of 4

How to prove $G_2$ is a normal subgroup of $G_1\times G_2$?

Big List of Fun Math Books

Chain rule and inverse in matrix calculus

Flipping Cards Probability