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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 18 |
| 3 | 195 |
| 4 | 1652 |
| 5 | 12825 |
| 6 | 96030 |
| 7 | 705341 |
| 8 | 5116200 |
| 9 | 36773397 |
| 10 | 262462010 |
| 11 | 1862790699 |
| 12 | 13160496684 |
| 13 | 92624149475 |
| 14 | 649794035142 |
| 15 | 4545979700445 |
| 16 | 31727803153232 |
| 17 | 220975193536845 |
| 18 | 1536191185018770 |
| 19 | 10661898343645847 |
| 20 | 73890140441316420 |
| 21 | 511405029708269529 |
[1,1,18,195,1652,12825,96030,705341,5116200, 36773397,262462010,1862790699,13160496684, 92624149475,649794035142,4545979700445, 31727803153232,220975193536845,1536191185018770, 10661898343645847,73890140441316420, 511405029708269529] |