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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 24 |
| 5 | 180 |
| 6 | 900 |
| 7 | 3780 |
| 8 | 14448 |
| 9 | 52164 |
| 10 | 181500 |
| 11 | 615780 |
| 12 | 2052072 |
| 13 | 6749028 |
| 14 | 21976500 |
| 15 | 71007300 |
| 16 | 228009696 |
| 17 | 728451972 |
| 18 | 2317445100 |
| 19 | 7346047140 |
| 20 | 23213772120 |
| 21 | 73156412196 |
| 22 | 229989358500 |
| 23 | 721474964100 |
| 24 | 2258832312144 |
| 25 | 7059480120900 |
| 26 | 22026886599900 |
[0,0,0,0,24,180,900,3780,14448,52164,181500, 615780,2052072,6749028,21976500,71007300, 228009696,728451972,2317445100,7346047140, 23213772120,73156412196,229989358500,721474964100, 2258832312144,7059480120900,22026886599900] |