Magic Cubes - The Basics

On this page we show features or characteristics common to all magic cubes. Many special magic cubes contain features that are unique to that type of cube. These features will be presented as we discuss the appropriate cubes.

Presentation

Several different methods may be used to show a magic cube on paper. While all of these are quite intuitive, I present them here for comparison.

	This is the traditional method. It was used by W.S. Andrews and others circa 1900. [1] [2] In recent years, the grid is often not used, so just the cell numbers are presented. The horizontal planes of the cube are shown, in reverse order, from top to bottom (plane 1 on the bottom). For smaller order cubes, the m planes are usually printed side by side to conserve vertical space on the page.
	This graphic illustration gives a clearer picture of the relationship of the numbers in the cube. This method of presentation is very good for cubes of low orders. However, for orders higher then 5 or 6, it is time consuming to prepare, and it becomes increasingly harder to follow the pillars and triagonals in the diagram.
	This method is favored by M. Trenkler. [3] (However, he also uses the first method, show above.) Notice that this displays vertical, instead of horizontal planes.

[1] W. S. Andrews, Magic Squares & Cubes, Open Court, 1908, 193+ pages.
[2] Hermann Schubert, Mathematical Essays and Recreations. Translated from German to English by Thomas J. McCormack, Open Court, 1899. 143+ pages.
[3] Marián Trenkler, A construction of magic cubes,   The Mathematical Gazette, 84(2000), 36-41,.

Basic Parts

There are 3m2 rows, columns and pillars in a magic cube. All are required to sum to the magic constant. There are 4 triagonals. All 4 must sum to the correct constant. These are the minimum requirements for a simple magic cube. There may be some diagonals that sum correctly, but that is not a requirement for a simple magic cube.

Orthogonal (planar) squares

The rows, columns, pillars, and triagonals may be considered the primary building blocks of a magic cube. They are the elements we are usually concerned with when constructing a magic cube.

However, when we wish to construct a cube with more advanced features, there is another element we must consider. That is the square arrays within the cube.
There are 2 types of square arrays. The first type are parallel to the sides of the cube and are often called orthogonal or planar squares. There are 3m squares of this type in a magic cube.
If  each of the 2 diagonals of one of these squares sum correctly, that square is magic.

The 2nd type of square array goes on the diagonal from the junction of 2 faces, through the center of the cube, to the junction of the opposite 2 faces. These will be discussed a little further down the page.

I have chosen to illustrate the planar squares by showing the central square in each direction. Obviously, there are central squares only if the cube is of odd order. Each cell in the cube is common to 3 squares. Here the 14 is common to all 3 central squares. The 20, for instance, is common to the top horizontal square, the front vertical square, and the central square parallel to the sides. In this order 3 cube, the only cells not included in the 3 central planar squares are the 8 corners of the cube. As the order of the cube increases the number of cells not included in the central planes becomes an ever greater percentage of the total cells

The horizontal planes are often used to present a magic cube on paper. For larger orders, it is much more practical then using the grid diagram.

Associated magic cubes

Reproduced here is the central horizontal plane of the above magic cube.

Notice that the rows and columns sum correctly to 42. Check the pair of numbers on opposite  sides of the central 14. In all cases the pair sums to 28 which is equal to m3 + 1 and 28 + 14 = 42, the magic constant of this cube. Because the pairs we checked include the 2 diagonals, this plane is an associated  magic square. This feature is common to the 3 central planes of all odd order associated magic hypercubes, regardless of order or dimension. So, if an odd order magic cube is associated, it contains at least 3 magic squares. BTW. All order 3 hypercubes are associated.

Associated magic squares and cubes are center-symmetric. There is much more information on these and other types of symmetrical cubes on my Self-similar cubes page.

Pandiagonal and semi-pandiagonal magic squares and cubes

Both main diagonals must sum correctly in order for a square to be considered magic.
The four main triagonals of a cube must sum correctly in order for the cube to be considered magic.

Pandiagonal and semi-pandiagonal magic squares and cubes are covered in much more detail and examples on my cube_semi-pan.htm page.
My cube_groups.htm page shows the relationships between simple, associated, pandiagonal/pantriagonal and semi-pan squares and cubes of order 4.

Oblique squares

The 2nd type of square array goes on the diagonal from the junction of 2 faces, through the center of the cube, to the junction of the opposite 2 faces.
There are 6 squares of this type in any cube, regardless of the order.

Above are the 3 pairs of oblique squares, with the complete grid shown for 1 square of each pair.

The most significant lines in these square arrays are the red lines. They are diagonals in these squares but are the triagonals of the cube. Actually, each triagonal appears as a diagonal in 3 oblique squares (6 squares time 2 = 12 and 12/3 = 4 triagonals).
The green lines are rows, columns or pillars in the orthogonal square arrays.

The oblique squares (planes) are not nearly as significant as the orthogonal ones are. However, they are another feature of a magic cube, and contribute to the total count of magic squares within the cube.

Broken oblique planes
Each of the six oblique planes has m-1 parallel planes that consist of two segments. these are analogous to the broken diagonals of a magic square.
And just as these broken diagonals sum correctly in a pandiagonal magic square, so are the planes correct (i.e. magic squares) in a perfect magic cube. In fact a perfect magic cube contains 9m pandiagonal magic squares.

To review characteristics of a magic cube.

• There are 3m orthogonal square arrays. Rows and columns and pillars must sum correctly, but diagonals need not.
  However in an odd order associated magic cube, the 3 central planes will have correct diagonals, meaning that these cubes contain at least 3 magic squares.
• There are 6 oblique square arrays in any type, and any order, of magic cube.
  Diagonals of these squares must sum correctly (they are the triagonals of the cube). Rows and columns of these arrays need not sum correctly.
• Higher types of magic cubes (not yet discussed) will contain varying numbers and types of magic squares.

Basic magic squares

There is 1 basic magic square of order 3. However, it may be shown in 7 other 'disguised' versions that are obtained by rotations and reflections. These 8 variations of the magic square are called aspects and are all considered equivalent when enumerating or comparing magic squares. Before 1675, Frénicle de Bessy listed all 880 basic solutions for the order 4 magic squares. To do so, he devised a method to determine which of the 8 aspects of each square should be called the basic square. There are only two simple rules to determine the basic square:

1. Rotate the magic square so that the cell in the top left corner of the square (the first cell of row 1) is the lowest value of all the corner cells.
2. If necessary, reflect the square around the leading diagonal so that the cell to the right of the top left corner is a lower value then the first cell of row 2.

Because there is just 1 order 3 square, indexing is rather irrelevant. Therefore, which is the basic magic square of this order is not important. However, for higher orders, this is an important concept! BTW Note that the order 3 magic square is associated, as per the statement made previously, that all order 3 hypercubes are associated.

Basic cubes and aspects

The order 3 magic square has 1 basic solution and 8 variations (aspects).
The order 3 magic cube has 4 basic solutions and 48 variations (aspects).

There are 8 possible corners of a magic cube, that may be placed lower, front, left. There are 3 rays extending from that corner which may be labeled in 6 different ways. That gives 8 times 6 = 48 variations due to rotations and reflections. [1]

The index for an order 3 cube consists of 4 numbers.
To normalize a magic cube to the standard position, there are 2 rules (actually 4 steps).

1. Rotate the cube so the smallest corner is in the bottom left front position.
2. Rotate/reflect as necessary so the 3 adjacent numbers to this corner are in the adjacent x, y, and z cells in increasing order of size.

This variation of the basic cube is simply a roll 90 degrees forward. What was the face is now the bottom. What was the back is now the top. The 4 red numbers in the bottom left of the basic cube are the numbers in the index, written 1, 15, 17, 23. Note that the center number remains constant (for odd orders) when the cube is rotated or reflected.

For all practical purposes, a cube is just as magic if it is a variation, rather then the basic cube. The value of basic position only becomes important when you wish to count or list the different cubes of a particular order.

Four numbers are required to define any of the 4 basic cubes of order 3. In fact, partly because order 3 is associated, it is possible to reconstruct the entire cube, if given these 4 initial numbers!
As the order becomes larger, more cell values will have to be included in the index string. However, no one yet has determined how many basic cubes there are even for order 4, so developing an index for higher orders has not yet become a necessity.

[1] John R. Hendricks, Inlaid Magic Squares and Cubes, 2^nd edition, self-published, 2000, 0-9684700-3-3, p. 134-136

Coordinates

This diagram illustrates the coordinates of some of the cells in an order 3 cube array. The coordinates serve as place names for specifying individual cells. Examples are shown of lines that must sum correctly, and an example diagonal, which need not sum correctly. Note that for rows, columns and pillars, 1 coordinate varies as you move along the line. For diagonals, 2 coordinates vary, and for triagonals, 3 coordinates vary as you move along the line. The underlined coordinates (in the lower left corner) are the locations for the 4 numbers of the index string.

One method of constructing magic cubes is to use coordinates in conjunction with modular equations.
This is a favored method of John R. Hendricks and is explained in many of his books. See [1]
It uses modular equations to form the m digits of a base m number for each cell. Each number is then converted to decimal and 1 is added  to get the final value for each cell.

[1] John R. Hendricks, Magic Squares to Tesseracts by Computer, self-published, 1998, 0-9684700-0-9

Species

Species is a consideration of how even and odd numbers are placed in order 3 normal magic hypercubes.
There is only 1 order 3 basic magic square, and so only 1 species, with the even numbers appearing at the 4 corners.
There are 4 basic order 3 magic cubes, but again there is only 1 species, because the magic cube must have all even numbers on 2 edges of  3 faces. Or just remember that  2 outside parallel faces (planes) each have 5 even numbers on 2 edges. The central parallel plane has the remaining 3 even numbers on one of its diagonals.
Or still another way to look at it. Each of the six faces has 1 odd number and 3 even numbers. 

Species 1 of 1 for magic square and cube

However, when we look at the 58 tesseracts (4-D hypercubes) we find that there are 3 different ways the even numbers are arranged. The example shown here, which John Hendricks has labeled species #1, appears in only 2 tesseracts. Species #2 is found in 24 tesseracts, with the remaining 32 tesseracts having species #3 .

No one has determined how many species there are for any of the order 4 hypercubes. A quick scan of order 4 magic squares seems to indicate that there are always 2 odd and 2 even numbers in the corners, making just two species; O, E, O, E and O, O, E, E.

[1] John R. Hendricks, Species of Third-Order Magic Squares and Cubes, JRM 6:3,1973, pp190-192.
[2] H.D. Heinz and J.R. Hendricks, Magic Square Lexicon: Illustrated, Self-published, 2000, 0-9687985-0-0

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Harvey Heinz   harveyheinz@shaw.ca
This page last updated October 14, 2009
Copyright © 2002 by Harvey D. Heinz