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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 13 |
| 3 | 108 |
| 4 | 736 |
| 5 | 4480 |
| 6 | 25344 |
| 7 | 136192 |
| 8 | 704512 |
| 9 | 3538944 |
| 10 | 17367040 |
| 11 | 83623936 |
| 12 | 396361728 |
| 13 | 1853882368 |
| 14 | 8573157376 |
| 15 | 39258685440 |
| 16 | 178241142784 |
| 17 | 803158884352 |
| 18 | 3594887626752 |
| 19 | 15994458210304 |
| 20 | 70781061038080 |
| 21 | 311711546474496 |
[0,1,13,108,736,4480,25344,136192,704512,3538944, 17367040,83623936,396361728,1853882368,8573157376, 39258685440,178241142784,803158884352, 3594887626752,15994458210304,70781061038080, 311711546474496] |