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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 8 |
| 5 | 44 |
| 6 | 290 |
| 7 | 2194 |
| 8 | 18690 |
| 9 | 177072 |
| 10 | 1848048 |
| 11 | 21079332 |
| 12 | 260998584 |
| 13 | 3487438476 |
| 14 | 50030096844 |
| 15 | 767092681992 |
| 16 | 12520306878720 |
| 17 | 216760973139072 |
| 18 | 3967857438205320 |
| 19 | 76575231882844056 |
| 20 | 1553981718941428824 |
| 21 | 33082675130470434336 |
| 22 | 737250032464248840192 |
[0,1,1,2,8,44,290,2194,18690,177072,1848048, 21079332,260998584,3487438476,50030096844, 767092681992,12520306878720,216760973139072, 3967857438205320,76575231882844056, 1553981718941428824,33082675130470434336, 737250032464248840192] |