004

There are four elementary arithmetic operations in mathematics: addition (+), subtraction (−), multiplication (×), and division (÷). Lagrange's four-square theorem states that every positive integer can be written as the sum of at most four squares.Four is one of four all-Harshad numbers. Each natural number divisible by 4 is a difference of squares of two natural numbers, i.e. 4 x = y 2 − z 2 {\displaystyle 4x=y^{2}-z^{2}}. A four-sided plane figure is a quadrilateral or quadrangle, sometimes also called a tetragon. It can be further classified as a rectangle or oblong, kite, rhombus, and square. Four is the highest degree general polynomial equation for which there is a solution in radicals.