Illustration for a(3)=33:
+------+------+------+------+------+------+------+
| | | | | | | |
| | | 18 | 17 | 26 | | 33 |
| | | | [4] | [13] | | |
+------+------+------+------+------+------+------+
| | | | | | | |
| | | | 1 | 3 | 5 | 28 |
| | | | | | | |
+------+------+------+------+------+------+------+
| | | | | | | |
| | 21 | 14 | 27 | 2 | 23 | |
| | | | [6] | | [11] | |
+------+------+------+------+------+------+------+
| | | | | | | |
| 22 | | 7 | | | 1 | 24 |
| | | | | | | [12] |
+------+------+------+------+------+------+------+
| | | | | | | |
| | 1 | 8 | 31 | 32 | | 25 |
| | | | [15] | [16] | | |
+------+------+------+------+------+------+------+
| 30 | 29 | | | | | |
| [20] | [19] | | | | | |
| [10] | [9] | | | | | |
+------+------+------+------+------+------+------+
Illustration for a(4)=46:
+------+------+------+------+------+------+------+------+------+------+------+------+
| | | | | | | | | | | | |
| 32 | | 37 | 44 | | | | | | | | |
| | | [15] | [22] | | | | | | | | |
+------+------+------+------+------+------+------+------+------+------+------+------+
| | | | | | | | | | | | |
| 24 | 8 | 7 | | | 39 | | | | 42 | | 29 |
| | | | | | | | | | | | |
+------+------+------+------+------+------+------+------+------+------+------+------+
| | | | 31 | | | | | | | | |
| | 16 | 1 | [13] | 18 | 21 | | | | 41 | 1 | 28 |
| | | | [6] | | | | | | | | |
+------+------+------+------+------+------+------+------+------+------+------+------+
| | | | | | | | | | | | |
| | 17 | | 2 | 3 | | | 43 | | 40 | | 27 |
| | | | | | | | | | [14] | | |
+------+------+------+------+------+------+------+------+------+------+------+------+
| | | | | | | | | | | | |
| | 36 | 19 | | 34 | 4 | 9 | 33 | 1 | 12 | 26 | |
| | | | | [1] | | | [10] | | | | |
+------+------+------+------+------+------+------+------+------+------+------+------+
| | | | | | | | | 46 | | | |
| | | | 20 | | 5 | | | [23] | | 38 | |
| | | | | | | | | [11] | | | |
+------+------+------+------+------+------+------+------+------+------+------+------+
| | | | | | | | | | | | |
| | | | 45 | 25 | 30 | 35 | | | | | |
| | | | | | | | | | | | |
+------+------+------+------+------+------+------+------+------+------+------+------+
|