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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 6 |
| 3 | 18 |
| 4 | 36 |
| 5 | 78 |
| 6 | 150 |
| 7 | 306 |
| 8 | 420 |
| 9 | 792 |
| 10 | 1338 |
| 11 | 2082 |
| 12 | 3228 |
| 13 | 4830 |
| 14 | 7050 |
| 15 | 9954 |
| 16 | 13920 |
| 17 | 18738 |
| 18 | 24666 |
| 19 | 32610 |
[0,0,6,18,36,78,150,306,420,792,1338,2082,3228, 4830,7050,9954,13920,18738,24666,32610] |