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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 11 |
| 4 | 48 |
| 5 | 341 |
| 6 | 2640 |
| 7 | 23561 |
| 8 | 228816 |
| 9 | 2674153 |
| 10 | 32749200 |
| 11 | 440019469 |
| 12 | 6504919080 |
| 13 | 102077649805 |
| 14 | 1724124159576 |
| 15 | 31359633592769 |
| 16 | 596774321099040 |
| 17 | 12048020039472209 |
| 18 | 259300490127149664 |
| 19 | 5798531237450331797 |
| 20 | 136619813565630980280 |
| 21 | 3380131718416134261301 |
[1,1,2,11,48,341,2640,23561,228816,2674153, 32749200,440019469,6504919080,102077649805, 1724124159576,31359633592769,596774321099040, 12048020039472209,259300490127149664, 5798531237450331797,136619813565630980280, 3380131718416134261301] |