About Number 4. Four is linear. It is the first composite number and thus the first non-prime number after one. The peculiarity of the four is that both 2 + 2 = 4 and 2 * 2 = 4 and thus 2^2 = 4. Four points make the plane of a square, an area with four sides. It is the simplest figure that can be deformed while keeping it's side lengths, such as the rectangle to parallelogram. Space let's us arrange equidistantly a maximum of four points. These then form a tetrahedron (tetrahedron), a body with four identical triangular faces. Another feature of the four is the impossibility of an algebraic equation of higher degree than four square roots using simple arithmetic and basic operations dissolve.
About Number 9. Nine is the smallest odd composite number and the minimum composite odd number that is no Fermat pseudoprime. It is the smallest natural number n, for each non-negative integer can be represented as a sum of at most n positive cubes (see Waring's problem), and the smallest positive integer n for which n squares in pairs of different positive edge length exist, the can be put together to form a rectangle. Number Nine is the number which (other than 0) as a single digit checksum generally occurs (in decimal number system) after multiplication by an arbitrary integer always even, and the number which is added to any other (except 0 and -9), as a single digit checksum the same result as the starting number itself - ie it behaves quasi-neutral.
What Is An Odd Number?
An odd number is an integer which is not a multiple of two. If it is divided by two the result is a fraction. One is the first odd positive number. The next four bigger odd numbers are three, five, seven, and nine. An integer that is not an odd number is an even number.
An even number is defined as a whole number that is a multiple of two. If an even number is divided by two, the result is another whole number. On the other hand, an odd number, when divided by two, will result in a fraction. Since odd and even numbers are defined only in reference to the set of integers (..., -3, -2, -1, 0, 1, 2, 3, ...), all negative numbers can also be either odd or even.