Primitive Perfect Isosceles Right Triangled Square

Title: _ 20:204AB GHM

Order: 20

Horizontal side: 204 Vertical side: 204

Elements: 1√2, 4√2, 8, 8√2, 16, 16√2, 32, 40, 42, 32√2, 40√2, 62, 80, 82, 84, 60√2, 61√2, 62√2, 80√2, 82√2.

Code: 847 0 204 800 84 204 801 164 204 402 204 164 401 204 204 826 122 82 46 0 120 87 4 124 86 4 116 167 12 124 166 12 108 327 28 124 326 28 92 627 60 124 626 60 62 427 122 124 602 60 60 825 122 0 12 61 61 610 61 61

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)