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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 17 |
| 3 | 120 |
| 4 | 885 |
| 5 | 6713 |
| 6 | 51932 |
| 7 | 407214 |
| 8 | 3224845 |
| 9 | 25733325 |
| 10 | 206584437 |
| 11 | 1666561042 |
| 12 | 13498994796 |
| 13 | 109713432390 |
| 14 | 894291885000 |
| 15 | 7307812510970 |
| 16 | 59847327807597 |
| 17 | 491062976039618 |
| 18 | 4036174402666925 |
| 19 | 33224883837921930 |
| 20 | 273873806179142545 |
| 21 | 2260338391869532332 |
[1,3,17,120,885,6713,51932,407214,3224845, 25733325,206584437,1666561042,13498994796, 109713432390,894291885000,7307812510970, 59847327807597,491062976039618,4036174402666925, 33224883837921930,273873806179142545, 2260338391869532332] |