Primitive Perfect Isosceles Right Triangled Square

Title: _ 20:342AC GHM

Order: 20

Horizontal side: 342 Vertical side: 342

Elements: 1, 1√2, 24√2, 30√2, 48, 34√2, 36√2, 60, 48√2, 68, 69, 70, 72, 68√2, 108, 136, 138, 137√2, 204, 171√2.

Code: 2045 0 138 1714 171 171 1376 205 205 346 171 171 695 205 136 1385 0 0 1081 108 138 485 108 90 484 156 90 723 204 66 12 205 137 13 205 136 707 204 136 1363 274 0 682 342 68 605 108 30 244 132 66 683 342 0 364 168 30 304 138 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)