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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 4 |
| 6 | 13 |
| 7 | 40 |
| 8 | 119 |
| 9 | 348 |
| 10 | 1014 |
| 11 | 2966 |
| 12 | 8726 |
| 13 | 25820 |
| 14 | 76823 |
| 15 | 229814 |
| 16 | 691186 |
| 17 | 2089850 |
| 18 | 6351448 |
| 19 | 19398726 |
| 20 | 59525641 |
| 21 | 183462778 |
| 22 | 567794458 |
| 23 | 1764118964 |
[0,0,0,0,1,4,13,40,119,348,1014,2966,8726,25820, 76823,229814,691186,2089850,6351448,19398726, 59525641,183462778,567794458,1764118964] |