Primitive Perfect Isosceles Right Triangled Square

Title: _ 20:90AB GHM

Order: 20

Horizontal side: 90 Vertical side: 90

Elements: 2, 4, 4√2, 6, 8, 9√2, 18, 13√2, 14√2, 24, 17√2, 18√2, 28, 24√2, 34, 36, 28√2, 33√2, 48, 36√2.

Code: 362 36 54 341 34 90 285 34 62 284 62 62 336 57 57 65 34 56 144 48 48 90 57 57 21 36 56 47 36 56 46 36 52 85 40 48 363 36 18 172 53 35 134 53 35 483 66 0 242 90 24 243 90 0 185 0 0 184 18 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)