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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 8 |
| 3 | 40 |
| 4 | 208 |
| 5 | 1088 |
| 6 | 5696 |
| 7 | 29824 |
| 8 | 156160 |
| 9 | 817664 |
| 10 | 4281344 |
| 11 | 22417408 |
| 12 | 117379072 |
| 13 | 614604800 |
| 14 | 3218112512 |
| 15 | 16850255872 |
| 16 | 88229085184 |
| 17 | 461973487616 |
| 18 | 2418924584960 |
| 19 | 12665653559296 |
| 20 | 66318223015936 |
| 21 | 347246723858432 |
| 22 | 1818207451086848 |
| 23 | 9520257811087360 |
[1,2,8,40,208,1088,5696,29824,156160,817664, 4281344,22417408,117379072,614604800,3218112512, 16850255872,88229085184,461973487616, 2418924584960,12665653559296,66318223015936, 347246723858432,1818207451086848,9520257811087360] |