A primitive Pythagorean triple is a Pythagorean triple
such that
,
where
is the greatest common divisor. A right
triangle whose side lengths give a primitive Pythagorean triple is then known
as a primitive right triangle.
Let
count primitive Pythagorean triples with perimeter
less than
,
counting the two orders of the legs only once. Lehmer (1900)
showed that
|
(1)
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|
(2)
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(OEIS A118858).