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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 9 |
| 4 | 58 |
| 5 | 330 |
| 6 | 1770 |
| 7 | 9198 |
| 8 | 46928 |
| 9 | 236736 |
| 10 | 1185645 |
| 11 | 5909805 |
| 12 | 29362806 |
| 13 | 145570230 |
| 14 | 720606705 |
| 15 | 3563543025 |
| 16 | 17610412600 |
| 17 | 86989143480 |
| 18 | 429579843435 |
| 19 | 2121099312195 |
| 20 | 10472653252550 |
| 21 | 51708363376950 |
| 22 | 255326054688320 |
[1,9,58,330,1770,9198,46928,236736,1185645, 5909805,29362806,145570230,720606705,3563543025, 17610412600,86989143480,429579843435, 2121099312195,10472653252550,51708363376950, 255326054688320] |