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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 7 |
| 3 | 53 |
| 4 | 399 |
| 5 | 3005 |
| 6 | 22631 |
| 7 | 170437 |
| 8 | 1283583 |
| 9 | 9666829 |
| 10 | 72802135 |
| 11 | 548282261 |
| 12 | 4129184367 |
| 13 | 31097419613 |
| 14 | 234198674759 |
| 15 | 1763780401765 |
| 16 | 13283257511391 |
| 17 | 100037924186797 |
| 18 | 753398499353143 |
| 19 | 5673941192219189 |
| 20 | 42731182342946895 |
[0,1,7,53,399,3005,22631,170437,1283583,9666829, 72802135,548282261,4129184367,31097419613, 234198674759,1763780401765,13283257511391, 100037924186797,753398499353143,5673941192219189, 42731182342946895] |