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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 48 |
| 5 | 276 |
| 6 | 1687 |
| 7 | 10750 |
| 8 | 70597 |
| 9 | 474478 |
| 10 | 3247844 |
| 11 | 22563904 |
| 12 | 158693152 |
| 13 | 1127661358 |
| 14 | 8083795761 |
| 15 | 58390722901 |
| 16 | 424562043703 |
| 17 | 3104994695198 |
| 18 | 22825260066996 |
| 19 | 168564068029385 |
| 20 | 1249985066423749 |
| 21 | 9303815610715531 |
| 22 | 69483859839881494 |
| 23 | 520527161650519576 |
[1,1,2,9,48,276,1687,10750,70597,474478,3247844, 22563904,158693152,1127661358,8083795761, 58390722901,424562043703,3104994695198, 22825260066996,168564068029385,1249985066423749, 9303815610715531,69483859839881494, 520527161650519576] |