15 = 3 x 5.
15 is a triangular number, the sum of the first five positive integers: 1 + 2 + 3 + 4 + 5 = 15.
7 can be partitioned in 15 ways.
A three-by-three magic square has the magic constant 15 (the sum of each row, column, or diagonal).
For n greater than 15, at least one number between n and 2n is the product of three different primes.
15 is a triangular number, the sum of the first five positive integers: 1 + 2 + 3 + 4 + 5 = 15.
7 can be partitioned in 15 ways.
A three-by-three magic square has the magic constant 15 (the sum of each row, column, or diagonal).
For n greater than 15, at least one number between n and 2n is the product of three different primes.
15 has a unique representation as a sum of four squares: 15 = 12 + 12 + 22 + 32.
15 is the smallest number that has three representations as a sum of three primes: 15 = 2 + 2 + 11= 3 + 5 + 7 = 5 + 5 + 5.
15 is the atomic number of the element phosphorus.
15 is the atomic number of the element phosphorus.
Source: Number Gossip
