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 870
- 870 is the smallest non-square that can be written as the sum of squares of some of its distinct prime factors
- 870 is the magic constant of a 12 by 12 magic square
- 870 is the smallest product of four different primes sandwiched between squarefree semiprimes (submitted by Massimo Kofler)
Rare Properties of 870
The number is called pronic if it is the product of two consecutive numbers.
They are twice triangular numbers.
Common Properties of 870
The number n is abundant if the sum of all its positive divisors except itself is more than n.
They are abundant above perfection, not to mention deficiency. See perfect and deficient numbers.
A positive integer greater than 1 that is not prime is called composite.
Composite numbers are opposite to prime 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 evil if it has an even number of 1's in its binary expansion.
Guess what odious numbers are.
The number n is practical if all numbers strictly less than n are sums of distinct divisors of n.
A number is said to be square-free if its prime decomposition contains no repeated factors.