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Hang Wu's user avatar
Hang Wu's user avatar
Hang Wu
  • Member for 7 years, 8 months
  • Last seen more than a week ago
21 votes
2 answers
2k views

2D Random Walk Hitting Time

6 votes
2 answers
770 views

Count Integers Not Greater Than $a$ Coprime To $b$

6 votes
1 answer
139 views

Is $a_{n+1}=\frac{a_n(a_n+n+k)}{n+1}$ eventually a non-integer, for all $k$?

5 votes
1 answer
105 views

The Cardinality of the Set $\{\lfloor\frac{N}{i^k}\rfloor \ | \ i \in \mathbb{Z}^+\}$ Given $k$

5 votes
1 answer
729 views

Counting Necklaces

4 votes
1 answer
115 views

Number of lattice points with the same parity inside a triangle

3 votes
1 answer
66 views

Calculate $\sum_{|S|=k}(n-|\cup S|)^m$ where $S$ is a subset of $X=\{\{a_1,a_2\},\{a_2,a_3\},\cdots,\{a_{n-1},a_n\},\{a_n,a_1\}\}$

3 votes
1 answer
443 views

Find the smallest positive integer $x$ satisfying $\gcd(x^n+a,(x+1)^n+a)>1$

3 votes
0 answers
236 views

Coupon Collector's Problem and Balls in Bins Variant

3 votes
1 answer
90 views

Calculate $\sum_{|\cup S|=k}(-1)^{|S|+1}$ where $S$ is a non-empty subset of $X=\{\{a_1,a_2\},\{a_2,a_3\}\cdots,\{a_n,a_{n+1}\}\}$

3 votes
4 answers
232 views

Multinomial Expansion

3 votes
1 answer
223 views

Series $\sum_{p \ prime}\frac{1}{1+p^2}$

3 votes
1 answer
566 views

Bell number modulo prime power

2 votes
0 answers
42 views

Transform generating function into linear recurrence relation

2 votes
0 answers
103 views

How many number of classes over matrices with $\pm 1$ entries are there, where equivalence means row/column permutation and multiplication?

2 votes
0 answers
45 views

Number of Sets of Points Containing a Given Point in its Convex Hull

2 votes
1 answer
32 views

$\prod_{i=1}^{p-1} (i^2+1) \equiv 4 \pmod p$ if $p$ is a prime $\equiv3\pmod 4$

2 votes
0 answers
32 views

Find $\prod_{i=1}^{p-1} (i^{2st}+1) \pmod p$ where $s<t$ are primes congruent to $1$ modulo $4$

2 votes
2 answers
597 views

Counting Perfect Powers [closed]

2 votes
2 answers
205 views

The Last Row of the Inverse of a Matrix

2 votes
0 answers
78 views

Shortest path inside the rectangle but not in the obstacle between two points

2 votes
2 answers
190 views

Calculating $\sum\limits_{i=1}^{n-1}\sum\limits_{j=1}^{m-1} |mi-nj|$

2 votes
0 answers
156 views

1D Random Walk Expected Hitting Time

2 votes
0 answers
113 views

Denest $\sqrt{5^{\frac{1}{3}}-4^{\frac{1}{3}}}$ [duplicate]

2 votes
1 answer
184 views

Probability that "abcdef" appears without "abcd" and "cdef"

1 vote
0 answers
29 views

Convert Arctangent Equality

1 vote
0 answers
119 views

Evaluating the Gauss Circle Problem $N(n)$ in $O(n^{\frac{1}{3}+\epsilon})$

1 vote
0 answers
39 views

Extended Euclidean Coefficients

1 vote
0 answers
39 views

Count the Number of Positive Integer Solutions to $\prod_{i=1}^{k}x_i\le N$

1 vote
0 answers
64 views

Coefficient of $x^k$ of the Taylor series of $\frac{1}{(1-x)^a (1+x)^b}$