Primitive Perfect Isosceles Right Triangled Square

Title: _d 18:136BD GHM

Order: 18

Horizontal side: 136 Vertical side: 136

Elements: 1√2, 2, 2√2, 11√2, 18, 14√2, 15√2, 18√2, 28, 32, 25√2, 36, 43, 50, 43√2, 68, 93, 68√2.

Code: 935 0 43 684 68 68 683 136 68 254 93 43 363 118 32 182 136 50 181 136 68 503 136 0 437 0 43 430 43 43 281 71 43 142 85 29 114 82 32 24 84 30 23 86 30 327 86 32 14 85 29 156 71 15

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)