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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 1 |
| 7 | 4 |
| 8 | 18 |
| 9 | 71 |
| 10 | 250 |
| 11 | 809 |
| 12 | 2484 |
| 13 | 7240 |
| 14 | 20341 |
| 15 | 55322 |
| 16 | 146237 |
| 17 | 376725 |
| 18 | 947555 |
| 19 | 2328999 |
| 20 | 5598888 |
| 21 | 13171906 |
| 22 | 30342861 |
| 23 | 68481058 |
| 24 | 151512767 |
| 25 | 328820214 |
[0,0,0,0,0,1,4,18,71,250,809,2484,7240,20341, 55322,146237,376725,947555,2328999,5598888, 13171906,30342861,68481058,151512767,328820214] |