Find all primes $p$, such that $p^p+2$ is also prime
Is $29$ the only prime of the form $p^p+2$?
When I restart httpd, I get the following error.  What am I missing?  [root@localhost ~]# service httpd restart Stopping httpd:                                            [  OK  ] Starting httpd: Syntax error on line 22 of /etc/httpd/conf.d/sites.conf: Invalid command 'SSLEngine', perhaps misspelled or defined by a module not included in the server configuration   I have installed mod_ssl using yum install mod_ssl openssh  Package 1:mod_ssl-2.2.15-15.el6.centos.x86_64 already installed and latest version Package openssh-5.3p1-70.el6_2.2.x86_64 already installed and latest version   My sites.conf looks like this  &lt;VirtualHost *:80&gt; #    ServerName shop.itmanx.com     ServerAdmin webmaster@itmanx.com      DocumentRoot /var/www/html/magento     &lt;Directory /var/www/html&gt;         Options -Indexes         AllowOverride All     &lt;/Directory&gt;      ErrorLog logs/shop-error.log     CustomLog logs/shop-access.log &lt;/VirtualHost&gt;  &lt;VirtualHost *:443&gt;     ServerName secure.itmanx.com     ServerAdmin webmaster@itmanx.com      SSLEngine on     SSLCertificateFile /etc/httpd/ssl/secure.itmanx.com/server.crt     SSLCertificateKeyFile /etc/httpd/ssl/secure.itmanx.com/server.key     SSLCertificateChainFile /etc/httpd/ssl/secure.itmanx.com/chain.crt      DocumentRoot /var/www/html/magento     &lt;Directory /var/www/html&gt;         Options -Indexes         AllowOverride All     &lt;/Directory&gt;      ErrorLog logs/shop-ssl-error.log     CustomLog logs/shop-ssl-access.log     &lt;/VirtualHost&gt; I received a mail today from Academia.edu (a site I wasn't previously aware of), asking me to confirm that I co-authored a paper with a colleague.  Having looked into it a little it sounds like it might be a useful site - the idea of a "social network for scientists" is one I've seen the need for in the past. However, partly due to bad experiences with the seemingly similar ResearchGate, I'm also skeptical.* Without signing up for an academia.edu account the site doesn't offer much information, so I would like the following information:   What specific features does academia.edu offer to its users? Is it genuinely useful for any of the following purposes (each of which seems genuinely needed)   as a platform for networking with academics for discovering relevant research as an effective system for post-publication peer review for organising references among a small team of people working on a project  Will it send out mails to my colleagues without my express and explicit permission? (I.e. are the mails I received today the result of a deliberate action by my colleague, who is aware that I will be emailed and wishes me to join the site; or are they essentially spam from a social networking site aggressively trying to expand its user base?) It's clear from its  that it's a private, venture-capital funded company. What is its business model?   In short, is this a site that has some genuine utility for academics, or should I just ignore it?  *I've never signed up for ResearchGate but I regularly receive spam from it purporting to be from my colleagues, who aren't aware that it's being sent on their behalf. I would be mortified if my senior colleagues received such mails claiming to be from me, so I won't touch it with a barge pole. How to mass rename files with ill-formed numbering? I've got bunch of files with ill-formed numbering:  prefix-#.ext       | for files with number 1-9 prefix-##.ext      | for files with number 10-99 prefix-###.ext     | for files with number 100-999   Due to further processing I need all of their names to be in format: prefix-###.ext. Is there any easy way to do that? "Please ask a new question" encourages question repetition for duplicates I just had a case of a user who re-posted his question because his first question was closed as a duplicate. And, logically, I closed his re-post as a duplicate of his original, asking him to edit his original and explain why it's not a duplicate, so we can reopen it.  This process has worked like that for years now, but suddenly I realized that with the new message, question repetition is even encouraged:     This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.   Clearly, a new user who finds their questions closed will now be happy to just post their question again and again, until it's not a duplicate anymore, instead of just fixing their original post.  We need to be more explicit about this, and show this message to the OP of the question:     If those answers do not fully address your question, please edit your question and explain why it is not a duplicate.   The original message should still be visible to other users and visitors, as they can't fix that question, of course. Why is cd not a program? Applying for a Canadian ETA after previous visits without one Changing data type in ArcGIS attribute table? How to remove specific elements in a numpy array Continuous bijection from $(a,b) \to S^1$? Over 20GB of disk space is gone? System drive, OS is Windows 7 x64 SP1 Ultimate.    Windows Explorer shows 100GB of used space.  TreeSizeFree shows 75GB of used space.  Total Commander and FAR confirm TreeSizeFree's measurements (counting hidden files).  Shadow copy is using up to 5GB with the current usage of 1.36GB.  Running FAR from Win7 PE shows the same.  Checkdisk shows no bad sectors. Disk is an OCZ SSD.  SMART monitor suggests SSD condition is perfect.    Where is the rest of space gone? If $k>0$ is a positive integer and $p$ is any prime, when is $\mathbb Z_p[\sqrt{k}] =\{a + b\sqrt k~|~a,b \in\mathbb Z_p\}$ a field. What does $(command) & do? I saw the following syntax in a bash script:   &gt;$(command) &amp;   I know that the ampersand &amp; at the end makes a command run in the background, but I have never seen it in combination with the dollar sign plus the brackets around the command.  What does it do? OpenLayers and OSGB 1936 (CRS 27700) I've been working with loads of shapefiles projected according to OSGB 1936 (CRS 27700). The project CRS is set to EPSG:27700 and "On the fly reprojection" to EPSG:27700 is set (I keep this as a default as I work with OSGB 1936 95% of my time).  I decided to download OSM layers from the OpenLayers plugin. When I load this, the EPSG in the bottom right of the screen goes from EPSG:27700 to EPSG:3857   Question 1: should this be happening anyway as it would suggest that the whole project has been re-projected to EPSG:3857?   As soon as the OSM layer is loaded it's way out of alignment but a quick pan seems to bring it altogether quiet nicely.   What I have noted is that (Question 2), if I try to re-specify the CRS to 27700, then the shapefiles "move" by a few tens of meters with respect to the OSM. Does this suggest that QGIS is doing a second re-projection (from what to what?)?   Also (Question 3), does it mean that if I import another shapefile that would be originally a dataset digitised with EPSG:27700 it would be re-projected to EPSG:3857 because the CRS in the bottom right of the screen was set to EPSG:3857 after the OSM import. This is all a bit confusing and logic would suggest that the import of a non-ESPG:27700 (project default CRS) should not go and change the EPSG setting in the bottom right of the screen. Anita Graser's book says on page 34 "Your project CRS will automatically be changed to Pseudo Mercator when you load a background map using the OpenLayers plugin option".   Does that mean there is no way of keeping ESPG:27700 active in the project when importing basemaps from OpenLayers? If so, what alternatives are there?  What I am trying to bottom out is to understand the correct way of importing basemaps (usually Google, Bing or OSM through the OpenLayers plugin) into my projects (always EPSG:27700) without losing alignment and getting layers to correctly re-project. I'm trying to support greater use of QGIS in my company but don't want to lose credibility by promoting the use of a tool that is misaligning datasets. Don't get me wrong. QGIS is a great tool and I am very fond of it but importing layers with different CRS's is quite common these days and getting this right from the start is half the job done.  I did quite an extensive Google search before posting and didn't come up with a recent, clear cut answer to my questions above. There is a bit of content out there on problems with older versions of QGIS, PROJ4, etc. but nothing recent for QGIS 2.0 so worth an update. I am an Indian living in Italy and I am going to the UK for a leisurely family vacation for about 10 days. Please note, this application is not very straight forward. There are four applicants, one applicant is applying from India another two are applying from Singapore and I am applying from Italy. The checklist at the top has the statement  all documents must be in English translated documents must be certified  I got the proof of accommodation from my commune, but it is in Italian. Getting it translated, isn't such a big deal as the commune itself provides multi-lingual certificates. For the rest of the documents, this is an issue. Such as for &quot;Evidence of being in education&quot;, my university provides an online certificate for this purpose which is in Italian. Multiple acquaintances said that they provided their Italian house contract (in Italian) as proof of residency and no requirement came up for translation. Can anyone comment on how strict are they while enforcing the translational requirements of documents in respect to a short term visitor visa? Can't save batch file shortly after running it on Windows 7 Error 404 : While using flag Recently on Stack Overflow I got privilege to flag a post. So when I try to flag a post as duplicate. The diaglog box is not properly loading.         However I am easily able to use other flag option like "other","spam" or "offensive".   "other"        "spam"        "offensive"        I am using Google Chrome Version 28.0.1500.71 and Win XP Operating System. I have tried in firefox as well but it is showing me same problem. How to calculate the difference between two dates using PHP? I have two dates of the form:  Start Date: 2007-03-24  End Date: 2009-06-26   Now I need to find the difference between these two in the following form:  2 years, 3 months and 2 days   How can I do this in PHP? I recently updated my profile bio (from Arqade) and clicked 'Save and copy changes to all public communities'. This appears to have broken/reset my profile picture on all but Arqade. Note that I did not update my profile picture as part of my changes. Arqade:  Meta SE for comparison:  I haven't touched my profile picture in years. Is this a bug?  Update: It appears my profile pic across all communities has been set back to 'Identicon'. I went on to Stack Overflow and changed my profile picture back to 'Gravitar' and clicked 'Save and copy to all communities' again, but this did not update my profile picture anywhere but SO. (I did the same on Sustainability to be doubly sure). Update 2: This is a persistent bug - I had changed most of my SE communities back to my 'Robotnik' display pic over the past little while. Today I edited my profile again on Arqade, Clicked 'Save and copy' - and the display pic reverted back to identicon again across all sites. Update 3: I have re-uploaded my profile picture and the 'Save and copy' function worked. It appears that this is actually a bug to do with the old images from Gravatar. If you go to  and are a 4k+ user on Anime.SE, you will see the following:        There is one reopen vote on this question, but the reopen vote count is displayed on a different line than the word "reopen". This is slightly silly, and would perhaps benefit from converting reopen (1) to reopen&amp;nbsp;(1), and likewise for close and delete votes. (Or any other way of preventing a line break between the vote type and the vote count.)  A repro (the close link) from here on Meta: How can I improve framerate of Minecraft client?