# 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 1913

- 1913 is the smallest prime p such that its next prime (1931) is an anagram of p
- 1913 is the smallest prime which is a concatenation of two 2-digit primes in a decreasing order
- 1913 is the smaller of the smallest pair of consecutive primes whose product of digits is equal and nonzero

## Common Properties of 1913

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.

A *prime* is a positive integer greater than 1 that is divisible by no positive integers other than 1 and itself.

Prime numbers are opposite to composite numbers.

A number is said to be *square-free* if its prime decomposition contains no repeated factors.