Gave myself a bit of a scare. My aNONradio stream cut out on me and when I went to investigate, I found the router dead. No lights. Nothing. Disconnectd the power cable from the back and re-attached.
Still nothing.
When I followed the power cord, I found that the wall wart seemed to have come mostly unplugged from the power bar. I have no idea what caused it to spontaneously disconnect, but I'm back now.
Isaac Kuo likes this.
![Is there a way of writing the expression<br>\[ \sum_{n=1}^m f(n) \]<br>in a way that omits the term where $n=a$?</p><p>I know it could be written as<br>\[ \left( \sum_{n=1}^m f(n) \right) - f(a) \]<br>but this doesn't work when $f(a)$ is undefined. Is there a way of writing the expression<br>\[ \sum_{n=1}^m f(n) \]<br>in a way that omits the term where $n=a$?</p><p>I know it could be written as<br>\[ \left( \sum_{n=1}^m f(n) \right) - f(a) \]<br>but this doesn't work when $f(a)$ is undefined.](https://social.jlamothe.net/photo/13528377976a61653463c9a386467268-1.png)

Darcy Casselman
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math.stackexchange.com/questio…
I'm gonna miss stack exchange.
Summation with exclusion
Mathematics Stack ExchangeJonathan Lamothe likes this.
imadeddinzaqout613
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Fish Face
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you will see a few variations on this if you look around. I would write it like this, but you can write basically anything unambiguous. You see notation like "a | n" or "g ∈ G" under summation symbols to represent summation over the divisors of n and elements of G, respectively, so it's pretty casual.
Jonathan Lamothe likes this.
Jonathan Lamothe
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