Seventeen

Seventeen (17) is the natural number following sixteen and preceding eighteen.

Seventeen is the 7th smallest prime number, and is a Fermat prime. The next prime is nineteen, with which it comprises a twin prime.

There are exactly seventeen two-dimensional space groups. These are sometimes called wallpaper groups, as they represent the seventeen possible symmetry types that can be used for wallpaper.

Seventeen is also

• The atomic number of chlorine.
• In the United States, the age at which one may donate blood and join the military voluntarily.
• The age at which one may view R-rated movies without a parent's accompaniment according to MPAA standards.
• The number of guns in a gun salute to U.S. Army, Air Force and Marine Corps Generals, and Navy and Coast Guard Admirals.
• The designation of United States Interstate 17, a freeway that in Arizona.
• In the title of At Seventeen, a famous song by Janis Ian.
• A swearword in Swedish. The origin is controversial; though it is also known in the form "Sjutton tusen jävlär". (Seventeen thousand demons.)
• In the Nordic countries the seventeenth day of the year is considered the heart and/or the back of winter.
• According to hacker's lore, 17 is described at MIT as `the least random number'.

See also: fifteen, sixteen, seventeen, eighteen, nineteen, integer, list of numbers.

This article is about the number. For the year AD 17, see 17. For the magazine Seventeen see Seventeen (magazine)