Primitive Perfect Isosceles Right Triangled Square

Title: _d 18:94AT GHM

Order: 18

Horizontal side: 94 Vertical side: 94

Elements: 2, 2√2, 4, 3√2, 6, 7√2, 10√2, 19, 20, 21, 17√2, 27, 20√2, 37, 47, 37√2, 57, 47√2.

Code: 575 0 37 474 47 47 473 94 47 104 57 37 36 64 44 65 67 41 271 94 47 70 64 44 41 71 41 22 73 39 21 73 41 215 73 20 193 73 20 377 0 37 370 37 37 174 54 20 204 74 0 203 94 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)