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Sep
30
awarded  Explainer
Sep
22
comment No simple closed form for Bell numbers
The premise of your question is somewhat unclear, because "closed form" is a somewhat variable quantity. Unless you allow factorials in a closed form, I can't think of any basic combinatorial quantity which has one. Allowing them lets in binomial coefficients and therefore Catalan numbers, but what else? Such basic combinatorial quantities as Stirling numbers and the partition function don't have well-known closed forms.
Sep
18
reviewed Reject suggested edit on How to find the components of a vector, given magnitude and angle?
Sep
15
reviewed Close What are the root of $x^3 - 2$ $\in \mathbb{R}[x]$?
Sep
13
reviewed Reopen condition for transitivity
Sep
12
revised Partial sums of Nicomachus' Triangle rows produce Stirling numbers of the 2nd kind?
added 1110 characters in body
Sep
12
answered Partial sums of Nicomachus' Triangle rows produce Stirling numbers of the 2nd kind?
Sep
11
revised 4-part partitions of n and 3n
deleted 90 characters in body; edited tags; edited title
Sep
11
answered Maximum value of $a+b$ given that $\frac{1}{a} + \frac{1}{b} = \frac{1}{20}$
Sep
10
reviewed Reject suggested edit on Sign of a series
Sep
5
reviewed Close Series expansion of $\log(1+x^2)$
Sep
2
answered a 2-regular graph is cyclic or not?
Aug
30
reviewed Close Prove a condition for a Banach algebra
Aug
30
answered Pushdown Automata and Challenge in Grammar
Aug
23
reviewed Leave Open Generating function for binomial coefficients $\binom{2n+k}{n}$ with fixed $k$
Aug
20
reviewed Close In how many ways can a number be expressed as a sum of squares of two natural numbers?
Aug
19
comment The Day Camp Stacking Game
Is rule 4 a repetition of rule 2 or is it trying to say something additional? (I assume that "clockwise" and "left" mean the same thing here).
Aug
17
reviewed Leave Closed Probability of ace in each hand
Aug
9
comment PRIMES is in P, Lemma 4.7: Why are $t$ roots in a polynomial of degree $< t$ a contradiction, if we don't know that the polynomial is not zero?
@Max, does the edited version convince you? If not, where does it fall short?
Aug
8
comment PRIMES is in P, Lemma 4.7: Why are $t$ roots in a polynomial of degree $< t$ a contradiction, if we don't know that the polynomial is not zero?
Expanded. The "notes" in the last paragraph of the proof would be more useful at the start.