Explanation 21x21 magic square

The 21x21 magic square is odd and a multiple of 3 (3 x 7 is simular as 3x5, 3x11, 3x13, 3x17, ... that is the 15x15, 33x33, 39x39, 51x51, ... magic square). It is possible to use 3x3 a proportional 7x7 panmagic square to construct a composite 21x21 magic square. Use a 7x3 (= 3x7) magic rectangle to construct an ultra magic 21x21 square.

Construction methods:

Methods to construct the 21x21 magic square are:

• Diagonal method
• Siamese method
• Knight movement method
• Symmetric transformation
• Lozenge method
• Composite, Simple a
• Composite, Simple b
• Composite, AxB compact
• Composite, Prop. (1) a
• Composite, Prop. (1) b
• Shift method (1)
• Shift method (2)
• Panmagic & 7x7 compact
• Ultra magic
• Pan 19x19 in 21x21 (1)
• Pan 19x19 in 21x21 (2)
• Concentric
• Concentric with diamond

The first seven methods lead to simple symmetric magic 21x21 squares.

Composite AxB compact, composite (1)a and composite (1)b give 21x21 magic squares with special magic features.

With the shift methods you can construct panmagic 21x21 squares. Shift method (2) gives a more tight structure.

It is also possible to use (as first grid) 9x the same 7x7 panmagic vierkant and 2 ternary grids (the third grid is a reflection of the second grid) to construct a panmagic and 7x7 compact 21x21 magic square.

Use a 7x3 (= 3x7) magic rectangle to construct an ultra magic 21x21 square, which is panmagic, symmetric, 3x3 and 7x7 compact.

Concentric [with diamond] and pan 19x19 in 21x21 are specials.