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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 3 |
| 5 | 7 |
| 6 | 5 |
| 7 | -1 |
| 8 | 9 |
| 9 | 10 |
| 10 | 12 |
| 11 | 13 |
| 12 | -1 |
| 13 | 11 |
| 14 | 14 |
| 15 | 15 |
| 16 | 24 |
| 17 | 19 |
| 18 | 25 |
| 19 | 22 |
| 20 | 21 |
| 21 | -1 |
| 22 | 23 |
[0,1,4,3,7,5,-1,9,10,12,13,-1,11,14,15,24,19,25, 22,21,-1,23] |