Euler brick
It has been suggested that Cuboid conjectures be merged into this article. (Discuss) Proposed since October 2020. 
In mathematics, an Euler brick, named after Leonhard Euler, is a rectangular cuboid whose edges and face diagonals all have integer lengths. A primitive Euler brick is an Euler brick whose edge lengths are relatively prime. A perfect Euler brick is one where the longest diagonal is also a whole number but such a brick has not yet been found.
Definition[edit]
The definition of an Euler brick in geometric terms is equivalent to a solution to the following system of Diophantine equations:
where a, b, c are the edges and d, e, f are the diagonals.
Properties[edit]
 If (a, b, c) is a solution, then (ka, kb, kc) is also a solution for any k. Consequently, the solutions in rational numbers are all rescalings of integer solutions. Given an Euler brick with edgelengths (a, b, c), the triple (bc, ac, ab) constitutes an Euler brick as well.^{[1]}^{:p. 106}
 At least two edges of an Euler brick are divisible by 3.^{[1]}^{:p. 106}
 At least two edges of an Euler brick are divisible by 4.^{[1]}^{:p. 106}
 At least one edge of an Euler brick is divisible by 11.^{[1]}^{:p. 106}
Examples[edit]
The smallest Euler brick, discovered by Paul Halcke in 1719, has edges (a, b, c) = (44, 117, 240) and face diagonals (d, e, f ) = (125, 244, 267).^{[2]} Some other small primitive solutions, given as edges (a, b, c) — face diagonals (d, e, f), are below:
( 85, 132, 720 ) — ( 157, 725, 732 ) ( 140, 480, 693 ) — ( 500, 707, 843 ) ( 160, 231, 792 ) — ( 281, 808, 825 ) ( 187, 1020, 1584 ) — ( 1037, 1595, 1884 ) ( 195, 748, 6336 ) — ( 773, 6339, 6380 ) ( 240, 252, 275 ) — ( 348, 365, 373 ) ( 429, 880, 2340 ) — ( 979, 2379, 2500 ) ( 495, 4888, 8160 ) — ( 4913, 8175, 9512 ) ( 528, 5796, 6325 ) — ( 5820, 6347, 8579 )
Generating formula[edit]
Euler found at least two parametric solutions to the problem, but neither gives all solutions.^{[3]}
An infinitude of Euler bricks can be generated with Sounderson's^{[4]} parametric formula. Let (u, v, w) be a Pythagorean triple (that is, u^{2} + v^{2} = w^{2}.) Then^{[1]}^{:105} the edges
give face diagonals
There are many Euler bricks which are not parametrized as above, for instance the Euler brick with edges (a, b, c) = (240, 252, 275) and face diagonals (d, e, f ) = (348, 365, 373).
Perfect cuboid[edit]
Unsolved problem in mathematics: Does a perfect cuboid exist? (more unsolved problems in mathematics)

A perfect cuboid (also called a perfect Euler brick, a perfect box) is an Euler brick whose space diagonal also has integer length. In other words, the following equation is added to the system of Diophantine equations defining an Euler brick:
where g is the space diagonal. As of September 2020^{[update]}, no example of a perfect cuboid had been found and no one has proven that none exist.^{[5]}
Exhaustive computer searches show that, if a perfect cuboid exists,
 the odd edge must be greater than 2.5 × 10^{13},^{[5]}
 the smallest edge must be greater than 5×10^{11}.^{[5]}
Some facts are known about properties that must be satisfied by a primitive perfect cuboid, if one exists, based on modular arithmetic:^{[6]}
 One edge, two face diagonals and the body diagonal must be odd, one edge and the remaining face diagonal must be divisible by 4, and the remaining edge must be divisible by 16.
 Two edges must have length divisible by 3 and at least one of those edges must have length divisible by 9.
 One edge must have length divisible by 5.
 One edge must have length divisible by 7.
 One edge must have length divisible by 11.
 One edge must have length divisible by 19.
 One edge or space diagonal must be divisible by 13.
 One edge, face diagonal or space diagonal must be divisible by 17.
 One edge, face diagonal or space diagonal must be divisible by 29.
 One edge, face diagonal or space diagonal must be divisible by 37.
In addition:
 The space diagonal is neither a prime power nor a product of two primes.^{[7]}^{:p. 579}
 The space diagonal can only contain prime divisors ≡ 1(mod 4).^{[7]}^{:p. 566}^{[8]}
Almostperfect cuboids[edit]
An almostperfect cuboid has 6 out of the 7 lengths as rational. Such cuboids can be sorted into three types, called Body, Edge, and Face cuboids.^{[9]}
In the case of the Body cuboid, the body (space) diagonal g is irrational. For the Edge cuboid, one of the edges a, b, c is irrational. The Face cuboid has just one of the face diagonals d, e, f irrational.
The Body cuboid is commonly referred to as the Euler cuboid in honor of Leonard Euler, who discussed this type of cuboid.^{[10]} He was also aware of Face cuboids, and provided the (104, 153, 672) example.^{[11]} The three integer cuboid edge lengths and three integer diagonal lengths of a face cuboid can also be interpreted as the edge lengths of a Heronian tetrahedron that is also a Schläfli orthoscheme. There are infinitely many face cuboids, and infinitely many Heronian orthoschemes.^{[12]}
Only recently have cuboids in complex numbers become known.
As of September 2017^{[update]} Randall L. Rathbun published^{[13]} 155,151 found cuboids with the smallest integer edge less than 157,000,000,000: 56,575 were Euler (Body) cuboids, 15,449 were Edge cuboids with a complex number edge length, 30,081 were Edge cuboids, and 53,046 were Face cuboids.
The smallest solutions for each type of almostperfect cuboids, given as edges, face diagonals and the space diagonal (a, b, c, d, e, f, g):
 Body cuboid: (44, 117, 240, 125, 244, 267, √73225)
 Edge cuboid: (520, 576, √618849, 776, 943, 975, 1105)
 Face cuboid: (104, 153, 672, 185, 680, √474993, 697)
 Complex Body cuboid: (63i, 60i, 65, 87i, 16, 25, √3344)
 Complex Edge cuboid: (√3344, 60, 63, 16, 25, 87, 65)
 Complex Face cuboid: (672i, 153i, 697, √474993, 185, 680, 104)
Perfect parallelepiped[edit]
A perfect parallelepiped is a parallelepiped with integerlength edges, face diagonals, and body diagonals, but not necessarily with all right angles; a perfect cuboid is a special case of a perfect parallelepiped. In 2009, dozens of perfect parallelepipeds were shown to exist,^{[14]} answering an open question of Richard Guy. Some of these perfect parallelepipeds have two rectangular faces. The smallest perfect parallelepiped has edges 271, 106, and 103; short face diagonals 101, 266, and 255; long face diagonals 183, 312, and 323; and body diagonals 374, 300, 278, and 272.
See also[edit]
Notes[edit]
 ^ ^{a} ^{b} ^{c} ^{d} ^{e} Wacław Sierpiński, Pythagorean Triangles, Dover Publications, 2003 (orig. ed. 1962).
 ^ Visions of Infinity: The Great Mathematical Problems By Ian Stewart, Chapter 17
 ^ Weisstein, Eric W. "Euler Brick". MathWorld.
 ^ Knill, Oliver (February 24, 2009). "Treasure Hunting Perfect Euler bricks" (PDF). Math table. Harvard University.
 ^ ^{a} ^{b} ^{c} Matson, Robert D. "Results of a Computer Search for a Perfect Cuboid" (PDF). unsolvedproblems.org. Retrieved February 24, 2020.
 ^ M. Kraitchik, On certain Rational Cuboids, Scripta Mathematica, volume 11 (1945).
 ^ ^{a} ^{b} I. Korec, Lower bounds for Perfect Rational Cuboids, Math. Slovaca, 42 (1992), No. 5, p. 565582.
 ^ Ronald van Luijk, On Perfect Cuboids, June 2000
 ^ Rathbun R. L., Granlund Т., The integer cuboid table with body, edge, and face type of solutions // Math. Comp., 1994, Vol. 62, P. 441442.
 ^ Euler, Leonard, Vollst¨andige Anleitung zur Algebra, Kayserliche Akademie der Wissenschaften, St. Petersburg, 1771
 ^ Euler, Leonard, Vollst¨andige Anleitung zur Algebra, 2, Part II, 236, English translation: Euler, Elements of Algebra, SpringerVerlag 1984
 ^ "Problem 930" (PDF), Solutions, Crux Mathematicorum, 11 (5): 162–166, May 1985
 ^ Rathbun, Randall L. (16 November 2018). "The Integer Cuboid Table". arXiv:1705.05929v3 [math.NT].
 ^ Sawyer, Jorge F.; Reiter, Clifford A. (2011). "Perfect parallelepipeds exist". Mathematics of Computation. 80 (274): 1037–1040. arXiv:0907.0220. doi:10.1090/s002557182010024007..
References[edit]
 Leech, John (1977). "The Rational Cuboid Revisited". American Mathematical Monthly. 84 (7): 518–533. doi:10.2307/2320014. JSTOR 2320014.
 Shaffer, Sherrill (1987). "Necessary Divisors of Perfect Integer Cuboids". Abstracts of the American Mathematical Society. 8 (6): 440.
 Guy, Richard K. (2004). Unsolved Problems in Number Theory. SpringerVerlag. pp. 275–283. ISBN 0387208607.
 Kraitchik, M. (1945). "On certain rational cuboids". Scripta Mathematica. 11: 317–326.
 Roberts, Tim (2010). "Some constraints on the existence of a perfect cuboid". Australian Mathematical Society Gazette. 37: 29–31. ISSN 13262297.