Primitive Perfect Isosceles Right Triangled Square

Title: _ 20:390AF GHM

Order: 20

Horizontal side: 390 Vertical side: 390

Elements: 5√2, 12, 64, 72, 82, 84, 64√2, 96, 108, 80√2, 82√2, 118, 128, 96√2, 144, 154, 164, 118√2, 123√2, 154√2.

Code: 1545 0 236 1544 154 236 820 308 390 821 390 390 723 226 236 845 226 224 1641 390 308 1182 118 118 1181 118 236 1087 118 236 123 226 224 960 214 224 961 310 224 802 390 144 1443 390 0 52 123 123 1281 246 128 642 310 64 641 310 128 1230 123 123

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)