8,661 reputation
21738
bio website gottwurfelt.wordpress.com
location San Francisco, CA
age 30
visits member for 4 years
seen 2 days ago

Quantitative analyst and math blogger.


Oct
10
answered Basic probability… probability that two users share a key out of a keypool of 20?
Oct
8
comment Recommend a statistics fundamentals book
FPP is definitely readable. (Incidentally, I'm currently teaching a course from it.) But it might be a bit low-level for this particular person.
Oct
8
comment complete $k$-ary tree: average distance between all vertices
I don't feel like thinking about this right now. But here's a sanity check: when $k$ is large, most leaves will be at level $r-1$ (i. e. the level furthest from the root) and most paths will require going all the way up to the root and all the way back down. So as $k$ approaches infinity with fixed $r$, your answer should approach $2r-2$.
Oct
3
awarded  Nice Answer
Oct
3
awarded  Editor
Oct
3
revised An interesting series
deleted 6 characters in body
Oct
3
answered An interesting series
Oct
1
comment How many disconnected graphs of the Rubik's cube exist?
For the related problem where you can move around the subcubes arbitrarily but can't peel off stickers, the answer is 12. The answer is surely much larger for your question, because you're allowing me to combine the stickers in arbitrary ways.
Oct
1
awarded  Enthusiast
Sep
30
comment How can you find the complex roots of i?
Or, if you want to emphasize that they're not real, you could refer to "complex roots of i".
Sep
29
answered How closely can we estimate $\sum_{i=0}^n \sqrt{i}$
Sep
20
comment Calulating length of cable running along exterior of an axle
I just want to point out that the answers given by REDace0 and by J. M. are the same, up to a change of notation.
Sep
17
comment Where to go after calculus?
You mentioned that you're transferring to another school. Would it be possible to contact someone there and ask them this question? In particular you'd get an answer that would mesh better with the curriculum you plan to enter.
Sep
14
comment Simplification of expressions containing radicals
Qiaochu, where does the $\pm 1/2$ in your guess come from?
Sep
13
answered Solving randomized recurrence relation
Sep
13
answered Mathematical concepts named after mathematicians that have become acceptable to spell in lowercase form (e.g. abelian)?
Sep
7
awarded  Civic Duty
Sep
6
comment $5^n+n$ is never prime?
In fact, if $\sum 1/log f(n)$ diverges and there's no covering set there should be infinitely many primes of form $f(n)$.
Sep
5
comment How to calculate the number of decimal digits for a binary number?
Just to confirm this for you: log(2)/log(10) is irrational. The proof is simple: clearly log(2)/log(10) is positive. So assume it's a positive rational number, i. e. that log(2)/log(10) = p/q where p and q are nonzero positive integers. Then you have p log 10 = q log 2. Exponentiating both sizes, 10^p = 2^q. But 10^p is divisible by 5 and 2^q isn't.
Sep
5
comment Finding a clever solution to a game of chance
This is a good method, but $\lim_{n \to \infty} q_n = 0$, right?