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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 1 |
| 6 | 5 |
| 7 | 17 |
| 8 | 39 |
| 9 | 155 |
| 10 | 745 |
| 11 | 4705 |
| 12 | 39573 |
| 13 | 369483 |
| 14 | 3970963 |
| 15 | 54943873 |
| 16 | 950039207 |
| 17 | 20417177215 |
| 18 | 545483266919 |
| 19 | 17663079620537 |
| 20 | 695250063366563 |
| 21 | 33778790635375371 |
[1,1,1,1,1,5,17,39,155,745,4705,39573,369483, 3970963,54943873,950039207,20417177215, 545483266919,17663079620537,695250063366563, 33778790635375371] |