Primitive Perfect Isosceles Right Triangled Square

Title: _ 20:90AU1of4 GHM

Order: 20

Horizontal side: 90 Vertical side: 90

Elements: 2, 5√2, 8, 10, 8√2, 9√2, 10√2, 16, 18, 20, 15√2, 16√2, 24, 30, 32, 24√2, 40, 42, 33√2, 66.

Code: 667 0 90 160 66 90 161 82 90 82 90 82 81 90 90 403 90 42 303 50 44 327 50 74 56 15 39 107 20 44 106 20 34 207 30 44 23 50 42 183 48 24 92 57 33 421 90 42 150 15 39 330 57 33 245 0 0 244 24 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)