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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 21 |
| 6 | 82 |
| 7 | 354 |
| 8 | 1671 |
| 9 | 8536 |
| 10 | 46814 |
| 11 | 273907 |
| 12 | 1700828 |
| 13 | 11158746 |
| 14 | 77057021 |
| 15 | 558234902 |
| 16 | 4230337018 |
| 17 | 33448622893 |
| 18 | 275322101318 |
| 19 | 2354401779494 |
| 20 | 20878592918183 |
| 21 | 191682453823420 |
| 22 | 1819147694792802 |
[1,0,1,2,6,21,82,354,1671,8536,46814,273907, 1700828,11158746,77057021,558234902,4230337018, 33448622893,275322101318,2354401779494, 20878592918183,191682453823420,1819147694792802] |