The numbers outside these twin triangles give the sum of the squares of the four figures of the adjacent sides:—
| 7 | ||||||
| 2 | 3 | |||||
| 135 | 99 | |||||
| 9 | 5 | |||||
| 1 | 8 | 6 | 4 | |||
| 117 | ||||||
| * | ||||||
| 137 | ||||||
| 6 | 4 | 2 | 9 | |||
| 5 | 1 | |||||
| 119 | 155 | |||||
| 7 | 8 | |||||
| 3 | ||||||
The twins are also closely allied on these points:—
18 is the common difference of 99, 117, 135, and of 119, 137, 155.
19 is the sum of each side of the upper triangle.
20 is the common difference of any two sums of squares symmetrically placed, both being on a line through the central spot.
21 is the sum of each side of the lower triangle.
10 is the sum of any two figures in the two triangles that correspond.
254 is the sum of 135, 119, of 117, 137, and of 90, 155.