What is special about square numbers here?
The final state of 1000 light bulbs switched on/off by 1000 people passing by
How do I force Windows to check for updates? What's the best way to communicate between view controllers? Fantasy novel about kid who controls magic through coin changer device I read this book in high school, and I can't remember what it's called. Some kid learns he has magical ability, but only finds out later that he controls it through some kind of coin changer he's been tinkering with the whole book. What and how does Darth Vader see? Are there any sources that talk about  about Darth Vader's visual acuity?  His life-supporting armour is quite advanced but does it provide any useful augmentation to his visual abilities? "Whether or not" vs. "whether" This will depend on whether he's suitable for the job.    This will depend on whether he's suitable for the job or not.   This will depend on whether or not he's suitable for the job.         It is still not defined whether we're following that approach.   It is still not defined whether we're following that approach or not.   It is still not defined whether or not we're following that approach.         "Or not" doesn't really seem to be needed to complement "whether". Why do people use it then? Is it redundancy and nothing more? Or is it for emphasis? Or are there cases when "or not" is required for the sentence to be grammatical? Particle energy in general relativity? Assume that a particle is moving with four-velocity $u^\mu$ through a spacetime with metric $g_{\mu\nu}$ ($-+++$ signature).  Let us also assume that there exists a time-like vector field $t^\mu=(1,0,0,0)$.  Is it generally true that the energy $E$ of a particle is given by the following expression:  \begin{eqnarray*} E &amp;=&amp; -mt_\mu u^\mu\\ &amp;=&amp; -mg_{\mu\nu} t^\nu u^\mu\\ &amp;=&amp; -mg_{00}u^0\\ &amp;=&amp; -mg_{00}\frac{dt}{d\tau}? \end{eqnarray*}  In the special case that $t^\mu$ is a Killing vector and $u^\mu$ is tangent to a geodesic then $E$ is a constant of motion of the particle. But the energy of a particle need not remain constant in the general case - is that true?  If $E=-mt_\mu u^\mu$ is indeed the particle mass/energy then does it act as a source of spacetime curvature given that it depends on the $00$-component of the spacetime metric ifself? I suppose that is not a problem. I have Blender 2.79 on my Windows 7 system.    I want to install 2.8, but I'm completing some courses which use 2.79.  If I install 2.8, will it automatically replace 2.79?  Will they interfere with one another?  Thanks. sqlplus doesn't work in Crontab /oracle/GR1/121/bin/sqlplus / as sysdba &lt;&lt;EOF &gt;&gt; $LOGFILE whenever sqlerror exit sql.sqlcode; set echo on; set serveroutput on; STARTUP; EXIT EOF   Already tried it with the path, but it hasn't worked. Notation for functions vs. numbers What is the difference between Halt and Shutdown commands? What is the difference between the halt and shutdown commands? Can I ask a postdoc who has closely supervised my research to write me a letter of recommendation? I have two Date values. I need to find number of weeks between them. I want to do it Apex Class. Not looking for formula fields.  So far I tried:  Integer numberofweeks = (projectStartDate - opp.Project_Start_Date__c)/7;    I receive this error:     Date arithmetic expressions must use Integer or Long arguments multisite: allow only specific users to update sites How can I identify what application is using a given file? What is the best term to describe the fact that most users have an initial dislike of any change to a UI even though it may really be net better over time?  Note: Question originally appeared How to enable top bar background opacity? There is a way to change top bar background opacity in ubuntu 20.04 lts.  I installed the hide top bar extension but is not a option to change it. Setting custom UITableViewCells height addtocontents not working with certain other packages This is a follow up question on   How do I change the toc dept mid document while using packages (in this case only mathtools).  An example:  \documentclass[a4paper,10pt,oneside]{book}  \usepackage{mathtools}  \begin{document}   \frontmatter             \chapter{hello}  \section{hello}  \subsection{hello}  \subsubsection{hello}   \setcounter{tocdepth}{3}  \tableofcontents   \mainmatter   \chapter{hello}  \section{hello}  \subsection{hello}  \subsubsection{hello}   \chapter{hello}  \section{hello}  \subsection{hello}  \subsubsection{hello}   \appendix   \addtocontents{toc}{\setcounter{tocdepth}{0}}   \chapter{hello}  \section{hello}  \subsection{hello}  \subsubsection{hello}   \chapter{hello}  \section{hello}  \subsection{hello}  \subsubsection{hello}  \end{document}   This example generates an error and very strangely puts an exclamation mark in the ToC as you can see here   however when I comment out the \usepackage{mathtools} it suddenly works again or replacing it with a different package such as \usepackage[T1]{fontenc} also generates no errors.  But this is not limited to just this specific package, certain other packages also introduce the same behavior (I just took this package to keep the example small). Please revoke badges gained by abusive voting In  (not feature request), :  ... if we find that people are abusing the system their accounts may get suspended. I would consider that kind of behavior abuse.  Well  sure qualifies. He has 11 Stack Exchange accounts and has in the last day spammed at least 8 of them to gain the Suffrage and sometimes Vox Populi badges. That's over 250 votes† in just a few hours! (And  -- while voting on other user's posts too.) I guarantee that he's not voting on those posts for/by their merits. Here's when he scammed the Suffrage badge per site (while also gaming the Vox Populi on some sites):                      - 2017-03-11 16:23:15Z                     - 2017-03-11 17:41:41Z                     - 2017-03-11 18:08:13Z                           - 2017-03-11 19:25:10Z                  - 2017-03-11 19:55:16Z                               - 2017-03-11 20:00:49Z               - 2017-03-11 20:03:13Z  - 2017-03-11 21:11:40Z  Note that he got the badge on three sites within an 8 minute span (but that might just be job run times). Please revoke badges gained through improper voting. And, maybe also warn/suspend such abusive voters.   † His account vote totals don't show all votes as some serial voting was reversed -- but none of the ill-gotten badges were. Call blocking for iPhone? How do I block unwanted callers without jailbreaking?