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seen Jan 9 '13 at 17:12

Oct
6
comment Extention of vector bundles on projective line: $Ext^1({\mathcal O_{\mathbb{P}^1}}(n),{\mathcal O_{\mathbb{P}^1}}(m))=$??
Yes, I have. But I think that computation of $Ext^1% as extension is difficult. Are you agree?
Aug
15
comment Prove that $ \frac{n}{\phi(n)} = \sum\limits_{d \mid n} \frac{\mu^2(d)}{\phi(d)} $
$\mu(d)$ and $\phi(d)$ multiplicative. Hence $\sum_{d \mid n} \frac{\mu^2(d)}{\phi(d)}$ also multiplicative. Left and right side are multiplicative. For $p^k$: $$\dfrac{p^k}{p^k-p^{k-1}}=1+\dfrac 1{p-1}$$
Aug
11
comment Summation of divergent series of Euler: $0!-1!+2!-3!+\cdots$
"For every fixed i, identify the coefficient of xi in the LHS and in the RHS." - How can this be used?
Aug
11
comment Summation of divergent series of Euler: $0!-1!+2!-3!+\cdots$
Numerical calculations in maple: for $x=0.7, n=10$ left-hand side is 0.6634301660, right-hand side is 0.6635102741.
Aug
11
comment Summation of divergent series of Euler: $0!-1!+2!-3!+\cdots$
$$\int\limits_0^{\infty}\dfrac{e^{-t}}{xt+1}dt=s_n(x)+o(x^n)$$
Aug
11
comment Graph isomorphism as permutation matrix.
$\pi M=M\pi$ is $M=\pi^{-1}M\pi$
Aug
11
comment Graph isomorphism as permutation matrix.
Why is not it obvious?
Aug
10
comment Showing $f(x)=\sum_{n=1}^{\infty}{\sin\left(\frac{x}{n^2}\right)}$ is continuous.
Or $\sum_{k=N}^{\infty}sin(x/k^2)<C\sum_{k=N}^{\infty}1/k^2\to 0$
Aug
10
comment Showing $f(x)=\sum_{n=1}^{\infty}{\sin\left(\frac{x}{n^2}\right)}$ is continuous.
But your inequality is uniform with respect to x!
Aug
10
comment Define integral for $\gamma,\zeta(i) i\in\mathbb{N}$ and Stirling numbers of the first kind
Sasha: Yes, thank you