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 Apr7 answered Picard Group Can Contain rational curve? Feb5 comment Links between Frobenius coin problem and the Postage Stamp problem? What do you want? You should provide a lot more detail and or background. What is an attainable number? What is a stamp? If we know these things, what do you want out of it? Feb5 awarded Citizen Patrol Feb5 comment What does it mean “diagram commutes”? en.wikipedia.org/wiki/Commutative_diagram Jan30 answered Solving Fulton and Harris exercise 2.4 Jan30 comment Solving Fulton and Harris exercise 2.4 Please provide the exercise number from Fulton–Harris. Jan23 answered group homomorphisms from the real line to infinite torsion abelian groups Jan23 comment group homomorphisms from the real line to infinite torsion abelian groups @user66257 — The group $\mathbb{R}$ is a $\mathbb{Q}$-vector space. (Maybe this helps to see why Eric Wofsey's comment is relevant.) Jan23 comment group homomorphisms from the real line to infinite torsion abelian groups Off-topic: why is there exactly one mathematical symbol in your question that deserves MathJaXification, while all the others have to be satisfied with plain cold sans-serif typesetting? Dec20 awarded Constituent Dec19 revised If $G/Z(G)$ is finite, then $|G'| < \infty$ Improves formatting Dec19 suggested approved edit on If $G/Z(G)$ is finite, then $|G'| < \infty$ Dec15 awarded Caucus Dec15 comment Maths to take a user chosen number to a predictable number See en.wikipedia.org/wiki/Collatz_conjecture. Ask them to run the computations until they stabilise. Definitely works for integers $\le 100$, and conjecturely for arbitrary positive integers. (Oops, I just remembered that it always ends in $\ldots,4,2,1,4,2,1,\ldots$; so maybe this is not a very good idea. Dec15 awarded Critic Dec15 comment $a_1^3+a_2^3+…+a_n^3=0 \Rightarrow a_1+a_2+…+a_n=0$ it is true or not? Please reconsider whether this should be tagged abstract-algebra. The tag description says: “Abstract algebra is the study of algebraic objects. Some of the more common algebraic objects are groups, rings, fields, vector spaces, modules, and other advanced topics.” Sep30 awarded Explainer Jun16 comment Irreducibility of $x^n-x-1$ over $\mathbb Q$ @Corvus — To echo TedShifrin, the polynomial ring $\mathbb{F}_{p}[X]$ is infinite, the set $\mathrm{Map}(\mathbb{F}_{p}, \mathbb{F}_{p})$ is finite. Hence the natural map $\mathbb{F}_{p}[X] \to \mathrm{Map}(\mathbb{F}_{p}, \mathbb{F}_{p})$ is not injective. To stress the difference, let me ‘prove’ that $\mathbb{F}_{2}$ is algebraically closed: Take a non-constant polynomial $f$, then $f$ is not constant $1$, and as $\mathbb{F}_{2}$ has only two elements, $f(x) = 0$ for some $x \in \mathbb{F}_{2}$. Thus $f$ has a zero, hence $\mathbb{F}_{2}$ is algebraically closed. $\square$ Spot the error. Jun3 comment When do we have that Absolute hodge classes= Hodge classes for complex projective manifolds? I think, if the Lefschetz operators are algebraic, then André's motivated cycles are algebraic. May27 comment A simpler expression that is always smaller or larger Well, write your function as $an^2 + bn + c$, where $a,b,c$ are fractions. Then it is already pretty simple. Next, you can consider if you want your estimate on a particular domain, or on all of $\mathbb{R}$. Depending on the answer, you might be able to round $a$ to an integer, and get rid of $b$ and $c$.