Primitive Perfect Isosceles Right Triangled Square

Title: __ 18:78AD GHM

Order: 18

Horizontal side: 78 Vertical side: 78

Elements: 2√2, 6√2, 11, 12, 15, 11√2, 12√2, 18, 20, 22, 24, 18√2, 20√2, 36, 27√2, 40, 29√2, 30√2.

Code: 302 30 48 241 24 78 122 36 66 274 51 51 296 49 49 123 36 54 155 36 51 64 30 48 363 36 18 117 36 51 110 47 51 24 49 49 227 36 40 403 58 0 202 78 20 203 78 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)