Primitive Perfect Isosceles Right Triangled Square

Title: _ 20:271AB GHM

Order: 20

Horizontal side: 271 Vertical side: 271

Elements: 29, 21√2, 34, 29√2, 34√2, 35√2, 38√2, 41√2, 58, 70, 76, 80, 58√2, 59√2, 92, 99, 80√2, 92√2, 99√2, 172.

Code: 1727 0 271 990 172 271 991 271 271 380 73 172 594 132 113 800 191 172 801 271 172 350 35 134 761 111 134 212 132 113 707 0 99 410 70 99 345 111 58 344 145 58 920 179 92 921 271 92 296 0 29 585 29 0 584 87 0 295 0 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)