It's tag-dependent. Blog posts tagged "bulletin" appear in the sidebar on sites that are considered technology sites (based on the sites listed in the footer) but not on others. Blog posts tagged "announcements" appear everywhere on the network (except on international sites). There's a third ...

As you know, MathOverflow has a special status in the Stack Exchange family, and (by a special agreement) it doesn't display any kind of ads nor links to the hot network questions in the sidebar. Would it be possible to remove also the links to the global meta questions in the "featured on meta" ...

It's given a prime $p$ with $p\equiv3\pmod4$. What shortcut (if any) is there to compute $x=2^{(p+1)/4}\bmod p$, compared to a general algorithm to compute $x=2^k\bmod p$ applied for $k=(p+1)/4$ ? I'm aware that $x^2\equiv-2\pmod p$ if $p\equiv3\pmod8$, and $x^2\equiv2\pmod p$ if $p\equiv7\pmod...