A tetractys, also called a tetraktys or decad, is an arrangement of 10 points in the form of a triangle with 1 point in the first row, two in the second, three in the third, and four in the fourth. It is therefore a representation of the triangular number . It also describes the arrangement of pins in bowling.

The tetractys was a mystical symbol that was important to the Pythagoreans.

See also

Bowling, Triangular Number

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Cite this as:

Weisstein, Eric W. "Tetractys." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Tetractys.html

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