10

The number "ten" originates from the Proto-Germanic root "*tehun", which in turn comes from the Proto-Indo-European root "*dekm-", meaning "ten". This root is the source of similar words for "ten" in many other Germanic languages, like Dutch, German, and Swedish. The use of "ten" in the decimal system is likely due to the fact that humans have ten fingers and ten toes, which people may have used to count by.

• A collection of ten items (most often ten years) is called a decade.
• The ordinal adjective is decimal; the distributive adjective is denary.
• Increasing a quantity by one order of magnitude is most widely understood to mean multiplying the quantity by ten.
• To reduce something by one tenth is to decimate. (In ancient Rome, the killing of one in ten soldiers in a cohort was the punishment for cowardice or mutiny; or, one-tenth of the able-bodied men in a village as a form of retribution, thus causing a labor shortage and threat of starvation in agrarian societies.)

• 10 is a composite number, the second squarefree semiprime, the fourth triangular number, and a happy number.{{Cite web |last=Weisstein |first=Eric W. |title=Happy Number |url=https://mathworld.wolfram.com/HappyNumber.html#:~:text=The%20first%20few%20happy%20numbers,97,%20100,%20... |access-date=2025-04-25 |website=mathworld.wolfram.com |language=en}}
• 10 is the smallest noncototient number.{{Cite web|author=

N. J. A. Sloane|author-link=Neil Sloane|url=https://oeis.org/A005278|title=A005278: Noncototients|website=The On-Line Encyclopedia of Integer Sequences|publisher=OEIS Foundation|access-date=2016-06-01}}

• There are exactly 10 small Pisot numbers that do not exceed the golden ratio.{{cite book | author=M.J. Bertin |author2=A. Decomps-Guilloux |author3=M. Grandet-Hugot |author4=M. Pathiaux-Delefosse |author5=J.P. Schreiber | title=Pisot and Salem Numbers | publisher=Birkhäuser | year=1992 | isbn=3-7643-2648-4 }}

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A ten sided polygon is called a decagon.

• The metric system is based on the number 10, so converting units is done by adding or removing zeros (e.g. 1 centimetre = 10 millimetres, 1 decimetre = 10 centimetres, 1 meter = 100 centimetres, 1 dekametre = 10 meters, 1 kilometre = 1,000 meters).
• The 10th element of the periodic table is neon.
• The 10th transition metal is zinc.

Image:Tetractys.svg]]

In Pythagoreanism, the number 10 played an important role and was symbolized by the tetractys.

• {{Portal-inline|Mathematics}}
• List of highways numbered 10

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Category:Integers