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1d
answered how to calculate derivative of $f_n(x)=f \circ f … \circ f(x)$? Derivative on $f \circ f_{n-1}$ or $f_{n-1} \circ f$?
2d
comment Infinite closed subset of $[0, 1]$ that does not have any subset of the form $[a, b]$ for $a< b$?
A nowhere dense set. en.wikipedia.org/wiki/Nowhere_dense_set
Jan
28
comment Is it correct? $1^n +2^n +…+(p-1)^n=-1 \pmod p$
Looks good to me.
Jan
20
revised Does there exists a function $f$ such that for some prime $p_1$, $p_{n+1}=f(p_n)$ gives a sequence of primes?
added 13 characters in body
Jan
20
asked Does there exists a function $f$ such that for some prime $p_1$, $p_{n+1}=f(p_n)$ gives a sequence of primes?
Jan
19
comment Show a function with integral is continuous
Do you know the Dominated Convergence Theorem?
Jan
11
comment Prove that $(a-b)^n\mid (a^n-b^n) \iff n=1$ under given conditions
Your conclusion that $a = b \mod (a-b)^n$ is incorrect. You took an $n$th root but those have multiple solutions mod $m$ in general.
Jan
11
comment Prove that $(a-b)^n\mid (a^n-b^n) \iff n=1$ under given conditions
@ElementaryNut Dude, there are way harder problems on MSE.
Dec
30
comment Is it necessary that normal subgroups must have an index of 2 always?
@DerekHolt I don't see why more "context" is needed. The OP is doing homework problems and clearly all the examples there involve normal groups of index two. All that's needed to answer the question is give some examples of when this doesn't occur.
Dec
30
comment Is it necessary that normal subgroups must have an index of 2 always?
There is no need to downvote this question or ask to close it! While it is a very (very) naive question it is a valid question. Given the close votes this convinces me that people do abuse the system.
Dec
28
comment Is there a closed form for $n^k$ in terms of $\Delta n^{k+1},\Delta n^k$, …?
It boils down to showing that the linear system (a matrix similar to $a_{ij}={i \choose j}$ for $i \leq j$ and zero otherwise) you have has a nonzero determinant.
Dec
27
comment Formula to calculate directly $ 1 + 2 \cdot 3 + 3 \cdot 4 \cdot 5 + 4 \cdot 5 \cdot 6 \cdot 7 + \dots + n \cdot (n+1) \cdot \dots \ (2n-1)$
Or bound by $1+1+1+\cdots \leq 1+ 2\cdot 3 + \dots$
Dec
24
awarded  Nice Question
Dec
23
revised $qx^2-px-q=0$ has no integer solutions
added 216 characters in body
Dec
23
revised $qx^2-px-q=0$ has no integer solutions
added 92 characters in body
Dec
23
revised $qx^2-px-q=0$ has no integer solutions
added 19 characters in body
Dec
23
answered $qx^2-px-q=0$ has no integer solutions
Dec
23
asked Simplest algorithm for edge coloring of a dodecahedron?
Dec
17
comment Can $\frac{P(x)s(x)+Q(x)}{R(x)}$ be a polynomial for some polynomial $s(x)$?
You want to compute solutions to Bezout's identity which I believe canbe done through Euclid's algorithm. en.wikipedia.org/wiki/B%C3%A9zout%27s_identity
Dec
17
comment $\lim_{n \to \infty} [a_n \cos(nx) + b_n \sin(nx)] =0$ implies $\lim_{n \to \infty} a_n = \lim_{n \to \infty} b_n = 0$
You need to use Egoroff's theorem instead and show that $\int_E \cos^2(nx) dx \to \frac{1}{2} m(E)$.