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 2421
- 2421 is the largest possible sum of three 3-digit primes that together use all non-zero digits 1 through 9
- 2421 = prime(2)2 + prime(4)4 + prime(2)2 + prime(1)1 and 2421 is the smallest number with this property (proved by Alexey Radul and David Wilson)
Common Properties of 2421
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 odd if it is not divisible by 2.
Numbers that are not odd are even. 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.