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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 21 |
| 4 | 220 |
| 5 | 3545 |
| 6 | 70566 |
| 7 | 1702267 |
| 8 | 48438104 |
| 9 | 1582227873 |
| 10 | 58475787850 |
| 11 | 2410935939731 |
| 12 | 109728296017572 |
| 13 | 5464423604085745 |
| 14 | 295562179335075758 |
| 15 | 17255009243888243115 |
| 16 | 1081438061864539992496 |
| 17 | 72422934220506772042817 |
| 18 | 5161269584065131270532242 |
[1,1,2,21,220,3545,70566,1702267,48438104, 1582227873,58475787850,2410935939731, 109728296017572,5464423604085745, 295562179335075758,17255009243888243115, 1081438061864539992496,72422934220506772042817, 5161269584065131270532242] |