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May
13
comment Evaulate/approximate a series formula $\sum_{i=1}^{n}\left ( \frac{1}{n}\right)^i \left(\frac{n-1}{n}\right)^{n-i}$
The sum isn't a binomial expansion because the binomial coefficients are missing.
Apr
5
awarded  Yearling
Mar
7
awarded  Good Answer
Feb
25
comment A non-nilpotent formal power series with nilpotent coefficients
@Gauloises Yes, it's not hard to check that the Freshman's Dream $(a+b)^2=a^2+b^2$, which holds in characteristic 2, extends to formal power series: $(\sum a_n x^n)^2=\sum a_n^2x^{2n}$
Feb
20
answered Even/Odd Binomial Coefficients
Feb
9
comment Binomial expansion (sort of ) rearrangement
I've added an extra step, hopefully this helps some. At the added step, I'm using the fact that the $k$-th power of a sum is the sum of products of ordered $k$-tuples of summands.
Feb
9
revised Binomial expansion (sort of ) rearrangement
added 141 characters in body
Feb
8
revised Why is the following subset of $\mathbb{C}$ simply connected.
deleted 4 characters in body
Feb
8
answered Why is the following subset of $\mathbb{C}$ simply connected.
Feb
8
answered Binomial expansion (sort of ) rearrangement
Feb
5
revised Proving an identity involving factorials
added 4 characters in body
Feb
5
comment Proving an identity involving factorials
The $a+b\leq n$ was a typo. I made an edit to fix that, and I tried to explain why the range of summation (in terms of $i$ and $j$) is $0\leq i,j\leq n$.
Feb
5
revised Proving an identity involving factorials
added 192 characters in body
Feb
5
revised Proving an identity involving factorials
deleted 1 character in body
Feb
5
revised Proving an identity involving factorials
deleted 8 characters in body
Feb
5
answered Proving an identity involving factorials
Jan
1
reviewed Approve harmonic-functions tag wiki
Jan
1
reviewed Approve harmonic-functions tag wiki excerpt
Jan
1
awarded  Custodian
Jan
1
reviewed Leave Closed Proving a subring of $\mathbb{Q}$ containing $\mathbb{Z}$ is a PID