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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 17 |
| 4 | 84 |
| 5 | 485 |
| 6 | 3236 |
| 7 | 24609 |
| 8 | 210572 |
| 9 | 2004749 |
| 10 | 21033900 |
| 11 | 241237001 |
| 12 | 3003349124 |
| 13 | 40345599957 |
| 14 | 581765196884 |
| 15 | 8963453118065 |
| 16 | 146969877361116 |
| 17 | 2555361954692189 |
| 18 | 46963373856864092 |
| 19 | 909707559383702169 |
| 20 | 18524816853636447380 |
| 21 | 395634467245613474981 |
[0,1,4,17,84,485,3236,24609,210572,2004749, 21033900,241237001,3003349124,40345599957, 581765196884,8963453118065,146969877361116, 2555361954692189,46963373856864092, 909707559383702169,18524816853636447380, 395634467245613474981] |