Primitive Perfect Isosceles Right Triangled Square

Title: _ 20:219AA GHM

Order: 20

Horizontal side: 219 Vertical side: 219

Elements: 6, 18, 20, 24, 18√2, 20√2, 30, 25√2, 36, 40, 30√2, 49, 67, 58√2, 85, 67√2, 103, 116, 85√2, 134.

Code: 1345 0 85 1161 116 219 582 174 161 1031 219 219 403 174 121 202 194 141 203 194 121 252 219 116 186 116 103 365 134 85 304 164 91 303 194 91 493 219 67 61 170 91 247 170 91 855 0 0 854 85 0 183 170 67 670 152 67 671 219 67

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)