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Jun
20
answered Combinatorial interpretation of identity: $\sum_{j=0}^b\binom{b}{j}^2\binom{n+j}{2b}=\binom{n}{b}^2$
Jun
20
answered Alternative way to count the number of solutions to the equation $x^2 + y^2 = -1$ over $\Bbb Z /p$
Jun
17
answered Counting the number of solutions of equation $x^2 + y^2 = 1$ over $\Bbb Z/p$
Mar
30
asked Counter-example to exponential law for locally compact [non-Hausdorff] spaces
Jan
11
answered A three variable binomial coefficient identity
Jan
10
answered Combinatorial Identity $ \sum_{k=1}^n (-1)^{k-1} \cdot q^{\frac{k(k-1)}{2}} \cdot \frac{\prod_{i=n-k+1}^n(1-q^i)}{\prod_{i=1}^k(1-q^i)} = 1 $
Jan
10
answered Finite summation with binomial coefficients, $\sum (-1)^k\binom{r}{k} \binom{k/2}{q}$
Jan
8
answered Is this morphism of spectra zero in the stable homotopy category?
Jan
3
answered Ramanujan-type trigonometric identities with cube roots, generalizing $\sqrt[3]{\cos(2\pi/7)}+\sqrt[3]{\cos(4\pi/7)}+\sqrt[3]{\cos(8\pi/7)}$
Dec
31
answered Proving $\sum_{k=0}^{2m}(-1)^k{\binom{2m}{k}}^3=(-1)^m\binom{2m}{m}\binom{3m}{m}$ (Dixon's identity)
Dec
31
answered Binomial Sum Related to Fibonacci: $\sum\binom{n-i}j\binom{n-j}i=F_{2n+1}$
Dec
30
answered Polynomial with a root modulo every prime but not in $\mathbb{Q}$.
Dec
30
answered How prove this $\prod_{1\le i<j\le n}\frac{a_{j}-a_{i}}{j-i}$ is integer
Dec
27
asked Combinatorial definition of Hall–Littlewood polynomials (sum over SSYT?)
Dec
26
answered Is there a “counting groups/committees” proof for the identity $\binom{\binom{n}{2}}{2}=3\binom{n+1}{4}$?
Dec
21
answered Evaluating Combination Sum $\sum{n+k\choose 2k} 2^{n-k}$
Dec
21
answered An example where $\frac{(2m)!(2n)!}{m!n!(m + n)!}$ is the number of ways of counting something?
Dec
20
answered Prove that for all non-negative integers $m,n$, $\frac{(2m)!(2n)!}{m!n!(m + n)!}$ is an integer.
Dec
20
answered What motiveted Gauss to formulate his theorem on quadratic reprocity?
Dec
13
asked Law of sines: uniform proof of Euclidean, spherical & hyperbolic cases