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Apr
15
awarded  Informed
Apr
14
revised Conjecture relating differential equation and sum of a function over partitions
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Apr
8
revised Erdos distance problem n=12
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Apr
6
awarded  Nice Answer
Apr
3
awarded  Excavator
Apr
3
revised series expansion of the q-Pochhammer symbol
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Mar
26
answered Is there an interesting species whose generating function gives the zigzag numbers?
Feb
23
comment Number of matrices with no repeated columns or rows
The problem of counting these matrices up to row and column permutations is solved in I. M. Gessel and J. Li, Enumeration of point-determining graphs, J. Combinatorial Theory Ser. A 118 (2011), 591-612, available online at arxiv.org/abs/0705.0042. (In the paper they are called "semi-point-determining bicolored graphs".) Of course, as in most unlabeled graphical enumeration problems, the formula is not simple, and might not be so helpful in deriving an asymptotic formula. The numbers in Richard's formula are sequence A181230 in the OEIS.
Feb
8
answered Exponential of a specific hypergeometric series
Feb
5
answered Exponential of a specific hypergeometric series
Jan
3
comment A problem on counting k-subsets of {-n,-n+1,…,n-1,n} satisfying that sum of elements equal to 0
You're right. I rewrote it to use the q-binomial theorem.
Jan
3
revised A problem on counting k-subsets of {-n,-n+1,…,n-1,n} satisfying that sum of elements equal to 0
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Jan
3
comment A problem on counting k-subsets of {-n,-n+1,…,n-1,n} satisfying that sum of elements equal to 0
I have rewritten my answer to make this clearer.
Jan
3
revised A problem on counting k-subsets of {-n,-n+1,…,n-1,n} satisfying that sum of elements equal to 0
deleted 4 characters in body
Jan
3
answered A problem on counting k-subsets of {-n,-n+1,…,n-1,n} satisfying that sum of elements equal to 0
Dec
27
comment Asymptotic growth for $\sum_{i=1}^{n-1}(n-i)\binom{k}{i}$
For $n>k$ the sum is equal to $(2^k-1)n -2^{k-1}k$ (by the binomial theorem) so Mathematica's asymptotic expansion isn't very helpful.
Dec
13
comment Quadratic transformation of hypergeometric function 2F1
It seems unlikely, but it would be difficult to prove that there is no such transformation.
Dec
10
comment Counting regular Hypergraphs
You can consider the problem of counting hypergraphs on n vertices with specified degrees of the vertices as counting partitions of a multiset in which each block is a set. Some references for this problem can be found in my paper Symmetric Functions and P-Recursiveness, J. Combin. Theory Ser. A 53 (1990), 257–285, people.brandeis.edu/~gessel/homepage/papers/dfin.pdf
Nov
27
awarded  Nice Answer
Nov
27
comment Combinatorial identities
Very nice proof!