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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 1 |
| 6 | 5 |
| 7 | 17 |
| 8 | 43 |
| 9 | 153 |
| 10 | 711 |
| 11 | 4787 |
| 12 | 36997 |
| 13 | 323223 |
| 14 | 3456487 |
| 15 | 47029493 |
| 16 | 778875019 |
| 17 | 15666901145 |
| 18 | 390119856899 |
| 19 | 11978383979491 |
| 20 | 447614381910255 |
| 21 | 20341843546977767 |
[1,1,1,1,1,5,17,43,153,711,4787,36997,323223, 3456487,47029493,778875019,15666901145, 390119856899,11978383979491,447614381910255, 20341843546977767] |