30 (number)

30 (thirty) is the natural number following 29 and preceding 31.

In mathematics

30 is the sum of the first four squares, which makes it a square pyramidal number.

It is a primorial and is the smallest Giuga number.

30 is the smallest sphenic number, and the smallest of the form 2 × 3 × r, where r is a prime greater than 3. 30 has an aliquot sum of 42; the second sphenic number and all sphenic numbers of this form have an aliquot sum 12 greater than themselves. The aliquot sequence of 30 is 16 members long, it comprises (30,42,54,66,78,90,144,259,45,33,15,9,4,3,1,0)

Thirty has but one number for which it is the aliquot sum: the square number 841.

Adding up some subsets of its divisors (e.g., 5, 10 and 15) gives 30, hence 30 is a semiperfect number.

30 is the largest number such that all coprimes smaller than itself, except for 1, are prime.

A polygon with thirty sides is called a triacontagon.

The icosahedron and the dodecahedron are Platonic solids with 30 edges. The icosidodecahedron is an Archimedean solid with 30 vertices, and the Tutte–Coxeter graph is a symmetric graph with 30 vertices.

Facebook features

Facebook is a social network service website launched on February 4, 2004. This is a list of software and technology features that can be found on the Facebook website.

Facebook structure

News Feed

On September 6, 2006, Ruchi Sanghvi announced a new home page feature called News Feed. Originally, when users logged into Facebook, they were presented with a customizable version of their own profile. The new layout, by contrast, created an alternative home page in which users saw a constantly updated list of their friends' Facebook activity. News Feed highlights information that includes profile changes, upcoming events, and birthdays, among other updates. This has enabled spammers and other users to manipulate these features by creating illegitimate events or posting fake birthdays to attract attention to their profile or cause. News Feed also shows conversations taking place between the walls of a user's friends. An integral part of the News Feed interface is the Mini Feed, a news stream on the user's profile page that shows updates about that user. Unlike in the News Feed, the user can delete events from the Mini Feed after they appear so that they are no longer visible to profile visitors. In 2011 Facebook updated the News Feed to show top stories and most recent stories in one feed, and the option to highlight stories to make them top stories, as well as to un-highlight stories. In response to users' criticism, Facebook later updated the News Feed to allow users to view recent stories first.