| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 0 |
| 3 | 4 |
| 4 | 8 |
| 5 | 56 |
| 6 | 304 |
| 7 | 2192 |
| 8 | 17408 |
| 9 | 156928 |
| 10 | 1568768 |
| 11 | 17257472 |
| 12 | 207087616 |
| 13 | 2692143104 |
| 14 | 37689995264 |
| 15 | 565349945344 |
| 16 | 9045599092736 |
| 17 | 153775184642048 |
| 18 | 2767953323425792 |
| 19 | 52591113145352192 |
| 20 | 1051822262906519552 |
| 21 | 22088267521037959168 |
| 22 | 485941885462833004544 |
[0,1,0,4,8,56,304,2192,17408,156928,1568768, 17257472,207087616,2692143104,37689995264, 565349945344,9045599092736,153775184642048, 2767953323425792,52591113145352192, 1051822262906519552,22088267521037959168, 485941885462833004544] |