Primitive Perfect Isosceles Right Triangled Square

Title: _ 20:72AC GHM

Order: 20

Horizontal side: 72 Vertical side: 72

Elements: 2√2, 4, 4√2, 8, 6√2, 9, 8√2, 12, 9√2, 14, 12√2, 18, 14√2, 15√2, 18√2, 27, 28, 27√2, 30√2, 36√2.

Code: 362 36 36 304 30 42 26 58 70 47 60 72 46 60 68 87 64 72 86 64 64 283 58 42 142 72 56 143 72 42 154 45 27 66 54 36 127 60 42 126 60 30 90 36 36 93 54 27 182 72 18 270 27 27 271 54 27 183 72 0

The properties below may precede order:side in a tiling's title:

• c = crossed. There is a tile-corner traversed by two lines. The only known crossed PPIRTS's below order 20 are 19:35AB1of4 and 19:35AB4of4.
• d = double-pentagon patterned. Every such tiling is a subdivision of an instance of the same deformable tiling by two 45-90-90-90-225 pentagons with a shared side, four triangles and two pseudotriangles. All below order 19 are degenerate in the sense that one or more sides of underlying tiles have shrunk to zero length. The non-degenerate d-tilings of order 19 are 19:221AA, 19:229AB and 19:241AA.
• e = elegant. No tile-corner is just a T-junction. Such tilings may be considered aesthetically pleasing. The only known elegant PPIRTS's below order 16 are 13:21AA, 14:26AJ, 14:35AA and 15:55AA.
• i = isomers exist which are ineligible for this catalogue. They are not included in the isomer count which follows 'of' in the tiling id.
• r = rectangular inclusion. The only known PPIRTS's below order 16 with a rectangular inclusion are 13:18AA1-4of4 and 15:44AA1-4of4.

Credit for Discovery

Just three people are credited with the discovery of Primitive Perfects:

Geoffrey H. Morley (GHM, England)

Jasper D. Skinner, II (JDS, United States)

William T. Tutte (WTT, Canada, 1917-2002) (15:44AI, 17:136AJ and 19:56AJ only)