# 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 325

- 325 is the smallest number that is the sum of 2 squares in exactly 3 ways
- 325 is the smallest triangular number that is the hypotenuse of a primitive Pythagorean triangle such that a leg of the triangle is also a triangular number
- 325 is the smallest and the only known 3-hyperperfect number
- 325 is the smallest odd unprimeable number — it can not be turned into a prime number by changing just one of its digits to any other digit

## Common Properties of 325

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.

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

Guess what odious numbers are.

A number is *odd* if it is not divisible by 2.

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

If you start with n points on a line, then draw n-1 points above and between, then n-2 above and between them, and so on, you will get a triangle of points. The number of points in this triangle is a *triangle* number.

Compare to square, pentagonal and tetrahedral numbers.