Reputation
10,921
Next privilege 15,000 Rep.
Protect questions
Badges
3 37 82
Newest
 Nice Answer
Impact
~127k people reached

Jun
17
revised Counting the number of solutions of equation $x^2 + y^2 = 1$ over $\Bbb Z/p$
P.S. about Weil etc
Jun
17
answered Counting the number of solutions of equation $x^2 + y^2 = 1$ over $\Bbb Z/p$
Jun
16
awarded  Nice Answer
Jun
15
reviewed Close Is being positive and orthogonal sufficient for being identity?
Jun
15
comment Counting the number of solutions of equation $x^2 + y^2 = 1$ over $\Bbb Z/p$
1) «Rational parametrization of conics»; 2) «Jacobi sums».
Jun
15
revised $SL_2(\mathbb Z_3)/Z(SL_2(\mathbb Z_3)) \cong \mathbb A_4$
edited tags
Jun
15
comment $SL_2(\mathbb Z_3)/Z(SL_2(\mathbb Z_3)) \cong \mathbb A_4$
From geometric POV the homomorphism to $A_4$ comes from the action of $SL_2(\mathbb Z_3)$ on 4-element set $P^1(\mathbb Z_3)$ (by fractional-linear transformations, if you will). Cf. $PSL_2(\mathbb F_4)\cong A_5$ etc.
Jun
7
comment Proof of $\sum_{n=1}^\infty \frac{1}{n^4 \binom{2n}{n}}=\frac{17\pi^4}{3240}$
related: math.stackexchange.com/q/144985
Jun
4
comment Why universal G-bundles are contractible?
If $B$ represents the functor «$X$ → principal $G$-bundles on $X$», then $E$ represents the functor «$X$ → principal $G$-bundles on $X$ with a fixed section». This functor is trivial, so $E$ is contractible.
May
14
comment Expected number of returns by time n in a symmetric 1-d random walk?
possible duplicate of Expected number of returns to zero in a symmetric random walk - closed form
May
13
comment Proving that $SL_2(\mathbb{Z}_5) / \{\pm I\}\simeq A_5$
cf. math.stackexchange.com/q/93762/152
May
6
comment Combinatorial definition of Hall–Littlewood polynomials (sum over SSYT?)
...but extracting something explicit for HL polynomials from that doesn't look like an easy task...
May
6
comment Combinatorial definition of Hall–Littlewood polynomials (sum over SSYT?)
Wikipedia page on Macdonald polynomials a) doesn't contain words 'semi-standard' or 'augmented'; b) doesn't give a combinatorial description of Macdonald polynomials — it mentions a description of transformed Macdonald polynomials that uses 'certain combinatorial statistics' inv and maj. I guess details can be found in arxiv.org/abs/math/0409538
Apr
10
comment A reference for a combinatorial identity
The second form looks like just a Vandermonde's identity ($\binom{i+k-1}i=\pm\binom{-k}i$ etc).
Apr
8
comment Stiefel-Whitney classes with Z-coefficients
(Re: The only problem I see is with the Steenrod square operation which may be undefined for integral coefficients) Well, yes there are no non-trivial stable operations from H(-;Q) to H(-;Q), after all...
Apr
7
reviewed Close Simplifying $\arctan\left(\frac{1}{\tan \alpha}\right)$
Apr
6
reviewed Leave Open Every prime is maximal in a Jacobson ring?
Apr
6
reviewed Close $\frac{1}{2}!$ aka $\Gamma(\frac{3}{2})$
Apr
5
reviewed Close Can modulo(remainder) be distribute over division?
Apr
5
reviewed Leave Open Evaluating $ \sum_{n=1}^\infty \frac{1}{n^2 2^n} $