It is the pythagorean triplet formula - (2m),(m^2 - 1),(m^2 + 1).
Triple comes right from the Pythagorean Theorem which states that for all integers a, b, and c, c2= a2 + b2
Example
52 + 122 = 132
The triple is (5, 12, 13)
Definition: Integers a, b, and c, such that a2 + b2= c2.
Plato, a Greek Philosopher, came up with a great formula for finding Pythagorean Triples
Plato's formula for Pythagorean Triples: (2m)2 + (m2 - 1)2 = (m2 + 1)2
To get a triple, just let m be any positive integer and do the math.
Let m = 2 for instance, we get:
(2m)2 + (m2 - 1)2 = (m2 + 1)2
(2× 2)2 + (22 - 1)2 = (22 + 1)2
(4)2 + (4 - 1)2 = (4 + 1)2
(4)2 + (3)2 = (5)2
Thus, the Pythagorean triple is (3, 4, 5)