Pythagorean triplet
A Pythagorean triplet is a set of three positiveintegers such that
That is, is a Pythagorean triplet if there exists aright triangle whose sides have lengths , , and ,respectively. For example, is a Pythagorean triplet.Given one Pythagorean triplet , we can produce another bymultiplying , , and by the same factor . It follows thatthere are countably many Pythagorean triplets.
Primitive Pythagorean triplets
A Pythagorean triplet is primitive if its elements arecoprimes
. All primitive Pythagorean triplets are given by
(1) |
where the seed numbers and are any two coprime positiveintegers, one odd and one even, such tht . If one presumes of the positive integers and only that , one obtains also many non-primitive triplets, but not e.g. . For getting all, one needs to multiply the right hand sides of (1) by an additional integer parametre .
Note 1. Among the primitive Pythagorean triples, the odd cathetus may attain all odd values except 1 (set e.g. ) and the even cathetus all values divisible by 4 (set ).
Note 2. In the primitive triples, the hypothenuses are always odd. All possible Pythagorean hypotenuses are contraharmonic means of two different integers (and conversely).
Note 3. N.B. that any triplet (1) is obtained from the square of a Gaussian integer as its real part
, imaginary part and absolute value
.
Note 4. The equations (1) imply that the sum of a cathetus and the hypotenuse is always a perfect square or a double perfect square.
Note 5. One can form the sequence (cf. Sloane’s http://www.research.att.com/ njas/sequences/?q=A100686&language=english&go=SearchA100686)
taking first the seed numbers 1 and 2 which give the legs 3 and 4,taking these as new seed numbers which give the legs 7 and 24, andso on.