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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 4 |
| 5 | 11 |
| 6 | 36 |
| 7 | 95 |
| 8 | 257 |
| 9 | 685 |
| 10 | 1747 |
| 11 | 4405 |
| 12 | 10601 |
| 13 | 25991 |
| 14 | 63589 |
| 15 | 156965 |
| 16 | 387971 |
| 17 | 973753 |
| 18 | 2471133 |
| 19 | 6340799 |
[0,0,0,4,11,36,95,257,685,1747,4405,10601,25991, 63589,156965,387971,973753,2471133,6340799] |