Primitive Perfect Isosceles Right Triangled Square

Title: _ 20:312AE GHM

Order: 20

Horizontal side: 312 Vertical side: 312

Elements: 12, 16, 16√2, 24, 32, 24√2, 40, 39√2, 56, 66, 78, 56√2, 90, 66√2, 78√2, 112, 144, 117√2, 168, 156√2.

Code: 1685 0 144 1564 156 156 1176 195 195 390 195 195 121 168 156 662 234 90 661 234 156 782 312 78 1445 0 0 1121 112 144 562 168 88 561 168 144 903 234 0 403 168 48 783 312 0 160 128 48 161 144 48 242 168 24 241 168 48 321 144 32

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)