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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 40 |
| 5 | 235 |
| 6 | 1476 |
| 7 | 11214 |
| 8 | 91848 |
| 9 | 859527 |
| 10 | 8710300 |
| 11 | 97675138 |
| 12 | 1179954612 |
| 13 | 15490520786 |
| 14 | 217602374458 |
| 15 | 3280028076615 |
| 16 | 52571985879600 |
| 17 | 895913825750191 |
| 18 | 16140560853800556 |
| 19 | 307048409240931810 |
| 20 | 6143666813617775100 |
| 21 | 129096480664676773542 |
| 22 | 2840750997343361802150 |
[0,1,2,9,40,235,1476,11214,91848,859527,8710300, 97675138,1179954612,15490520786,217602374458, 3280028076615,52571985879600,895913825750191, 16140560853800556,307048409240931810, 6143666813617775100,129096480664676773542, 2840750997343361802150] |