Primitive Perfect Isosceles Right Triangled Square

Title: _ 20:72AB GHM

Order: 20

Horizontal side: 72 Vertical side: 72

Elements: 1, 2, 2√2, 4, 5, 17, 14√2, 20, 15√2, 16√2, 23, 17√2, 25, 26, 27, 20√2, 30, 32, 23√2, 26√2.

Code: 327 0 72 170 32 72 171 49 72 237 49 72 236 49 49 156 0 40 305 15 25 164 31 39 20 47 55 21 49 55 146 31 39 275 45 26 41 49 53 202 20 20 17 45 26 260 46 26 261 72 26 51 20 25 257 20 25 203 20 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)