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Joel Cohen's user avatar
Joel Cohen's user avatar
Joel Cohen's user avatar
Joel Cohen
  • Member for 13 years, 1 month
  • Last seen more than a week ago
48 votes
Accepted

Is there an equation to describe regular polygons?

43 votes

Continuity of the roots of a polynomial in terms of its coefficients

38 votes

Is a Sudoku a Cayley table for a group?

21 votes
Accepted

Can we differentiate Fermat's little theorem?

17 votes

How to prove those "curious identities"?

16 votes
Accepted

Determine the number of functions $f: \mathbb{Z}_{p^n} \to \mathbb{Z}_{p^n}$

16 votes

Why $\sqrt{-1 \times -1} \neq \sqrt{-1}^2$?

15 votes

Why is it that Complex Numbers are algebraically closed?

15 votes
Accepted

Is the reciprocal of an analytic function analytic?

15 votes
Accepted

Does $f(z+2\pi)=f(z)$ for all $z\in \mathbb{C}$?

15 votes
Accepted

Show that $\mathbb{Z}_{2} \times \mathbb{Z}_{4}$ is not a cyclic group

13 votes
Accepted

Summation of complex numbers

12 votes
Accepted

Factorial division using Pascal's triangle.

11 votes
Accepted

Putnam problem of the day, roots of a polynomial

11 votes
Accepted

What is a Number Theorist

11 votes
Accepted

Is $\mathbb{Z}_2 \times \mathbb{Z}_4^\infty$ isomorphic to $\mathbb{Z}_4^\infty$?

10 votes
Accepted

Is there a representation of an inner product where monomials are orthogonal?

10 votes

orthonormal polynomials

10 votes

A "naive" proof approach for the convergence of $(n!)^2/(2n)!$

9 votes

Is this inverse limit of groups of roots of unity the Prüfer group?

8 votes

Test for convergence of the series $\sum\limits_n\ln\left(1+\frac{1}{n^2}\right)$?

8 votes
Accepted

Yugoslavia team selection for IMO 1987 (functions)

7 votes

Is it possible to find a companion matrix of a polynomial which is also hermitian?

7 votes
Accepted

questions about unipotent radical

7 votes

Motivation for triangle inequality

7 votes
Accepted

Is $\mathbb{R}$ equipotent to $\mathbb{R}^2$?

6 votes

Detecting a negative coefficient in a power series

6 votes
Accepted

How does extending a field affect matrix similitude?

6 votes
Accepted

Write down a $\mathbb Q$-Basis for $\mathbb Q(\alpha, i)$ and show that $\mathbb Q(\alpha, i) = \mathbb Q(\alpha + i)$.

6 votes

Puzzle: Dropping balls along the way

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