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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 7 |
| 4 | 41 |
| 5 | 252 |
| 6 | 1675 |
| 7 | 11634 |
| 8 | 83181 |
| 9 | 608818 |
| 10 | 4539896 |
| 11 | 34364253 |
| 12 | 263355143 |
| 13 | 2039370396 |
| 14 | 15933107322 |
| 15 | 125436559380 |
| 16 | 994121046225 |
| 17 | 7924935634275 |
| 18 | 63504334502998 |
| 19 | 511233121598277 |
| 20 | 4132727837100768 |
| 21 | 33533674854227400 |
[1,1,1,7,41,252,1675,11634,83181,608818,4539896, 34364253,263355143,2039370396,15933107322, 125436559380,994121046225,7924935634275, 63504334502998,511233121598277,4132727837100768, 33533674854227400] |