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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 22 |
| 4 | 140 |
| 5 | 969 |
| 6 | 7084 |
| 7 | 53820 |
| 8 | 420732 |
| 9 | 3782992 |
| 10 | 32389076 |
| 11 | 275617830 |
| 12 | 2350749914 |
| 13 | 20140518790 |
| 14 | 173429992350 |
| 15 | 1500850805160 |
| 16 | 14550277251918 |
| 17 | 133009333771170 |
| 18 | 1198324107797254 |
[1,1,4,22,140,969,7084,53820,420732,3782992, 32389076,275617830,2350749914,20140518790, 173429992350,1500850805160,14550277251918, 133009333771170,1198324107797254] |