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Oct
20
awarded  Great Question
Sep
9
answered Fields, closed under two operations
Aug
5
comment Expected length of a sequence that contains all words of a given length.
@ByronSchmuland I think that's the same ref leonbloy cited at the end of his answer below.
Aug
5
revised Determine whether the argument is valid or invalid
typesetting cleanup
Aug
5
answered Determine whether the argument is valid or invalid
Aug
4
comment N white and black balls and N boxes Probability
Given $N$ new users posting $N$ new questions which are worded as demands rather than questions, what is the probability they are all homework problems?
Jul
17
awarded  Popular Question
Jun
29
comment Fibonacci sequence - how to prove $a_n=\frac{1}{\sqrt{5}} ((\frac{1+\sqrt{5}}{2})^n-(\frac{1-\sqrt{5}}{2})^n)$ without induction
This is given as a warmup in the free text by Wilf called generatingfunctionology.
Jun
28
comment How to find generator in a finite group?what is generator?
When I said, "suppose you can factor" the "you" is the OP who is (presumably) a human trying to solve a problem. I did not (and would not) say "suppose a factorization exists for $(p-1)$".
Jun
28
answered How to find generator in a finite group?what is generator?
Jun
25
awarded  Informed
Jun
24
comment practical arithmetic in prime factorizations
Ross, I don't get your answer. You seem to be reiterating his idea rather than answering his question regarding the use of this technique in actual software.
Jun
24
revised practical arithmetic in prime factorizations
added 91 characters in body
Jun
24
answered practical arithmetic in prime factorizations
Jun
16
revised How many expected people needed until 3 share a birthday?
added 208 characters in body
Jun
15
revised Probability (usage of recursion)
added 325 characters in body
Jun
15
revised Probability (usage of recursion)
added 325 characters in body
Jun
15
answered Probability (usage of recursion)
Jun
15
comment How to show that $\sum\limits_{k=1}^{n-1}\frac{k!k^{n-k}}{n!}$ is asymptotically $\sqrt{\frac{\pi n}{2}}$?
@PeterR: Often mathematicians will use "elementary" to mean "does not use complex analysis". As you can see, "elementary" does not mean "easy."
Jun
15
comment The sum $\sum\limits_{n \ge 0} \binom{m-1}{n} \frac{n!}{m^n} + \binom{n+1}{2}\binom{m-1}{n-1}\frac{(n-1)!}{m^n}$ is asymptotic to $\sqrt{9πm/8}$
Interesting. This immediately gives that three collisions occur in less than an expected $2 \sqrt{\pi m/2} = \sqrt{2\pi m}$. (In fact, I will guess that it's $15/8 \sqrt{\pi m/2}$.) Since $\sqrt{2\pi m}$ is the square root of the circumference of a circle of radius $m$, there is clearly a geometric proof we're missing. :)