# Number Gossip

(Enter a number and I'll tell you everything you wanted to know about it but were afraid to ask.)

## Unique Properties of 512

- 512 is the smallest power of 2 of the form 2
^{n} such that both 2^{n} - n^{2} and 2^{n} + n^{2} are prime
- 512 is the smallest integer (except 1) which is the cube of the sum of its digits
- 512 is the smallest cube that is a sum of a positive cube and a positive square (512 = 169 + 343)

## Rare Properties of 512

The number n is a *cube* if it is the cube of an integer.

A number is a *power of 2* if it is 2 to some power.

## Common Properties of 512

A positive integer greater than 1 that is not prime is called *composite*.

Composite numbers are opposite to prime numbers.

The number n is *deficient* if the sum of all its positive divisors except itself is less than n.

Compare with perfect and abundant numbers.

A number is *even* if it is divisible by 2.

Numbers that are not even are odd. Compare with another pair -- evil and odious numbers.

The number n is *odious* if it has an odd number of 1's in its binary expansion.

Guess what evil numbers are.

An integer n is *powerful* if for every prime p dividing n, p^{2} also divides n.

How much power? They all can be written as a^{2} b^{3}.

The number n is *practical* if all numbers strictly less than n are sums of distinct divisors of n.