$(2n)!+1$ is not a perfect square for $n > 2$?
$n!+1$ being a perfect square
Why are there two tensions on my free body diagram? A man sits on a platform attached to a pulley and pulls himself up as shown (ignore the angle of the rope - it should be vertical). Apparently, the man/platform object has a force of 2T pulling it up. Why is it not just T?  Much appreciated! If I want to add more RAM to my computer, how can I buy something compatible? What kinds are there? How do I determine which kind my computer will accept and how much I can add? Show that given seven real numbers, it is always possible take two of them, such that $\left\vert\frac{a-b}{1+ab}\right\vert<\frac{1}{\sqrt{3}}$ Show that given seven real numbers, it is always possible take two of them, such that $$\left\vert\frac{a-b}{1+ab}\right\vert&lt;\frac{1}{\sqrt{3}}$$   The "Pigeonhole principle" states that if $n$ items are put into $m$ containers, with $n &gt; m$, then at least one container must contain more than one item, but how I an define my "container" such that meets the condition of the problem? Answer didn't load temporary "Which" vs. "what" — what's the difference and when should you use one or the other? Most of the time one or the other feels better, but every so often, "which" vs. "what" trips me up.   So, what's the exact difference and when should you use one or the other? Cycle Normal Pass in Camera Space I've just downloaded a CD image of Ubuntu. I know the installer has a check CD option, but how can I check that the image is good before burning it to CD? Attending an academic conference is what type of travel? I am planning to travel to Portugal to attend an academic conference and in that regard needed a short-stay Schengen visa. The visa application has a field "Purpose of Travel" with the following options:   - Business - Sports - Cultural - Other - Study - Visiting family or friends - Medical reasons - Official visit - Transit - Airport transit - Tourism   I am attending the conference to present the research I am conducting as a part of my PhD. So "Study" is the closest in my opinion. But I don't want the Embassy to misconstrue that it is for studying at a university in Portugal. In that case, would "Business" be the right option to choose? How can I reproduce the error "package... needs to be reinstalled, but I can't find an archive for it" for testing? From time to time, Ubuntu users encounter errors from  or , of the form:  The package some-package needs to be reinstalled, but I can't find an archive for it.  I want to know what causes this error so that I can reproduce it and try to find safe ways of fixing it, even when the broken package is important and has many dependencies.  of the  might give a bit of a clue, but I don't know how packages get the status that causes the error.  How can I produce this error for testing on my (Ubuntu MATE 17.10) system?  This is prompted by  and my long-standing discomfort with closing questions about this error against , whose answer uses dpkg --force-all to remove the offending package.  suggests this solution has worked for many users, but I am not confident that using --force-all won't cause later problems, or that it's a good idea to use this method to remove important packages like APT. After reading an article about Ubuntu's netflix support I decided to try running netflix through chromium but I got this error code: M7063-1913 I assumed that it was a problem with html5 but in the playback preferences it doesn't give me the option to use it. Why is the second order perturbative correction to the ground state energy always down? Could it be a structure of "How many -singular noun- is there?" We had an argument in our collage if it's possible to have such structure:     "How many -singular noun- is there?"   For example:      How many chair is there?   The claim of the supporters: This structure should be used in case that t is not known whether there is one one or more chairs there. While just in case that it is known certainty that there are more than one chair, it should be "how many chairs are there".    The claim of the opponents: This structure cannot be since using the phrase "how many" always should be with a plural noun.  Both sides are not native English speakers, then I would like to know what is the truth. How do I save the output of a command to a file?  Is there a way without using any software? I would like to know how. Listing multiple compound words How do I list multiple things that are compound words?  In my own language I'm used to writing these lists like this:  "I kicked foot-, basket-, and volleyball"  The sentence is supposed to mean that I kicked all types of balls (football, basketball and volleyball). However, it does not seem correct to me. Should I write them as whole words, with or without hyphen, or how? In the following method definitions, what does the * and ** do for param2?  def foo(param1, *param2): def bar(param1, **param2): How to remove the "No front page content has been created yet." message from the front page? I only want blocks on the homepage. Because I don't have any nodes, and I want to keep the homepage as /node I am getting a "No front page content has been created yet." message on my page.  How do I get around this? Aiming at specific body parts Is Adzerk safe / legitimate? undelete big files - mission impossible? I've accidentaly deleted outlook.pst (6.7GB) file, while there was only 400MB free space left on primary NTFS partition (winxp).  I've tried several recovery tools to get this file back. "Ontrack Easy Recovery Pro" found 0 pst files (complete scan mode), while "Recover My Files" in sector scan mode found 5 pst's, but 4 of them of sizes from 3 to 28 KB, while the 5th one - 1Gb.  I've managed to succesfuly recover 1Gb pst file, which was 1 year old copy (the one used after the latest windows reinstall).  Now, I'm frustrated and confused   Why 1 year old file was succesfuly recovered if there were only 400MB left on primary partition? Where's 6.7GB file gone? I did some reading (), and it seems that there's almost no probability to retrieve the file I'm looking for, but wait - none of recovery tools i've used found zero-sized pst file, moreover - if due to fragmentation a file might be corrupted - we could use scanpst.exe to fix some errors and survive with 10 or 100 emails missing - whatever. Could you please recommend some more sophisticated recovery tools for this particular task?   Appretiate your help - thanks in advance Calendar month view is unresponsive on iOS 9