511

Why 511 is special

Same number, different meanings

How 511 is understood across different contexts — never implying one meaning because of another.

• Mathematics

  511 is what a hotel or airport Wi-Fi network should return before you log in. It exists so software can tell the difference between 'the internet is broken' and 'you have not accepted the terms yet' — a distinction that matters to any app retrying in the background. Most portals still just redirect instead.

• Science

  511 Davida is among the largest main belt asteroids, roughly 300 kilometres across, and has never been visited, which is unusual for an object of that size.

• Technology & computing

  511 exists so software can distinguish 'the network is broken' from 'you have not accepted the hotel Wi-Fi terms'. Background apps retrying against a portal that redirects instead cannot tell the difference and either hammer the network or fail silently. Most portals still redirect.

Not just a mathematical number

511is also used in ways where ordinary arithmetic doesn't apply — each listed below with what genuinely does and doesn't follow from it.

• Mathematical number

  A genuine quantity — its mathematical properties (prime, square, factors, and so on) are real facts about it.

  A genuine quantity that ordinary arithmetic applies to — it can be prime, even, a perfect square, added to another number meaningfully, and so on.

• Code

  Also used as a code — HTTP status codes.

  An assigned identifier from a fixed registry or standard — its digits don't represent an amount, and arithmetic on it is meaningless (HTTP status 404 + 1 is not a 'better' status; it's a different, unrelated code).