Четыре__

This website is titled "Четыре__" and its description is "chetyre__". The keywords for this website include the number "four" and related mathematical concepts such as "tetrahedral number", "second tetrahedral number", "maximal power of a quadratic equation", "second triform number", and "quarter". The website contains a reference to the Wikipedia page for the number four, which includes information about its properties as a number and its significance in mathematics. The website also includes a saved copy and links to access more information from the original source.