Primitive Perfect Isosceles Right Triangled Square

Title: _ 20:312AK GHM

Order: 20

Horizontal side: 312 Vertical side: 312

Elements: 2√2, 4, 4√2, 8, 8√2, 14, 15, 14√2, 27, 28, 42, 57, 57√2, 99, 114, 99√2, 156, 114√2, 198, 156√2.

Code: 1985 0 114 1564 156 156 1563 312 156 421 198 156 285 198 128 574 255 99 573 312 99 145 198 114 144 212 114 20 226 128 40 224 126 41 228 126 275 228 99 80 220 122 81 228 122 1145 0 0 1144 114 0 153 228 99 990 213 99 991 312 99

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)