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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 1 |
| 6 | 3 |
| 7 | 16 |
| 8 | 85 |
| 9 | 434 |
| 10 | 2271 |
| 11 | 11530 |
| 12 | 58400 |
| 13 | 290689 |
| 14 | 1436685 |
| 15 | 7036418 |
| 16 | 34286464 |
| 17 | 166316979 |
| 18 | 804557406 |
| 19 | 3884248150 |
| 20 | 18731033958 |
| 21 | 90269841924 |
| 22 | 434955114981 |
| 23 | 2096028083116 |
| 24 | 10104206901987 |
| 25 | 48733744753173 |
| 26 | 235196202817401 |
| 27 | 1135892957109815 |
| 28 | 5490007141743186 |
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