Tob Ernack's user avatar
Tob Ernack's user avatar
Tob Ernack's user avatar
Tob Ernack
  • Member for 8 years, 6 months
  • Last seen this week
12 votes

Factorise $x^5+x+1$

12 votes

Find all the functions $f:\mathbb{Z}^+ \to \mathbb{Z}^+$ such that $f(f(x)) = 15x-2f(x)+48$.

11 votes
Accepted

How to create a cubic equation that include sums of the roots of another cubic equation

9 votes
Accepted

On a conjecture that if $2\left(p_n+p_{n-1}\right)\equiv -1\pmod {n^2}$ then $n=11$ only.

8 votes

What's the closest approximation to $\pi$ using the digits $0-9$ only once?

8 votes
Accepted

Calculating the discriminant

7 votes
Accepted

Elements of $\mathbb Q(2^{1/3})$

6 votes
Accepted

Irreducible monic polynomial in $\mathbb{Q}[x]$

6 votes

Primes congruent to $1$ modulo $6$ are of the form $3a^2+b^2$

6 votes
Accepted

Describing the Galois group of $\mathbb{Q}(\sqrt{2},\sqrt{3})$ without computing the extension degree (proof check please)

6 votes
Accepted

How to prove that $\sum_{n=1}^{231}\sec^{4}\left(\frac{2\pi n}{231}\right)=949167681$?

5 votes
Accepted

Can it happen that an irreducible degree $2$ polynomial becomes a perfect square in the algebraic closure?

5 votes

How do we show that $(10^{10})!$ is larger than $10^{10^{10}}$?

5 votes
Accepted

Summation of $\sum_{k=1}^{n}\sin^{2}kx$

5 votes
Accepted

Show that every person gets a suitable job

4 votes
Accepted

Integrating $e^{-x^2}x^2$

4 votes

How one can prove $\prod_{k=1}^{n-1} (\cos\theta-\cos(k\pi/n)) = 2^{1-n}\sin(n\theta)\csc\theta$?

4 votes

Is there a polynomial mod $p$?

4 votes
Accepted

How to approximate real numbers using members of $\mathbb Z (\sqrt d)$?

4 votes
Accepted

Compute limit of double exponent expression.

4 votes
Accepted

$f=x^4+1$ is reducible over infinite field $F$ with characteristic $p>0$

4 votes

Is there an infinite product of reals in $(0,1)$ that doesn't converge to $0$?

4 votes
Accepted

Under what circumstances is it acceptable to assume all variables will be equal in optimization problems?

4 votes
Accepted

Does the tangent line really touch a single point?

4 votes

Weird result to a differential equation

4 votes
Accepted

What subset of the reals have unique prime factorizations if you allow rational exponents?

3 votes

Show that $3^{7^n}+5^{7^n}\equiv 1 \pmod{7^{n+1}}$

3 votes

Show that $3^{7^n}+5^{7^n}\equiv 1 \pmod{7^{n+1}}$

3 votes

Boundary defining function

3 votes
Accepted

Smooth maps between manifolds with boundary: restricting the codomain to a submanifold with boundary