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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 15 |
| 5 | 96 |
| 6 | 665 |
| 7 | 6028 |
| 8 | 60907 |
| 9 | 725560 |
| 10 | 9591549 |
| 11 | 142574004 |
| 12 | 2323440119 |
| 13 | 41519079616 |
| 14 | 803667844993 |
| 15 | 16797423268252 |
| 16 | 376458083887875 |
| 17 | 9014414549836296 |
| 18 | 229564623594841637 |
| 19 | 6197477089425914692 |
| 20 | 176767174407208663759 |
| 21 | 5312208220728020517136 |
| 22 | 167760328500471584529321 |
[1,1,1,4,15,96,665,6028,60907,725560,9591549, 142574004,2323440119,41519079616,803667844993, 16797423268252,376458083887875,9014414549836296, 229564623594841637,6197477089425914692, 176767174407208663759,5312208220728020517136, 167760328500471584529321] |