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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 25 |
| 4 | 73 |
| 5 | 673 |
| 6 | 3025 |
| 7 | 20329 |
| 8 | 107929 |
| 9 | 653425 |
| 10 | 3674017 |
| 11 | 21516217 |
| 12 | 123214825 |
| 13 | 714258241 |
| 14 | 4113149041 |
| 15 | 23770767625 |
| 16 | 137113121593 |
| 17 | 791700344593 |
| 18 | 4568824885825 |
| 19 | 26373938451289 |
| 20 | 152222238686089 |
| 21 | 878652055801825 |
[0,1,1,25,73,673,3025,20329,107929,653425,3674017, 21516217,123214825,714258241,4113149041, 23770767625,137113121593,791700344593, 4568824885825,26373938451289,152222238686089, 878652055801825] |