------+------+-----+-----+-----+-------- 7x + 6x = 13x
| | | 7 | 11 | 20 | |
| | 4 +-----+-----+ | |
| 3 | | 8 | 12 | 26 ----- | |
| +-----+-----+-----+ | | |
| | | 9 | 13 | 27 2x ----- |
2 +------| 5 +-----+-----+ | |
| | | 10 | 14 | 28 ----- |
| |-----+-----+-----+ |
| 4 | | 11 |15,18| 29,30,31,32 ←---4x-----
| | 6 +-----+-----+
| | | 12 | 19 | 36 ←--- 35,34,33 are missing
------+------+-----+-----+-----+-------
| | | 13 | 20 | {38}
| | 7 +-----+-----+