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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 120 |
| 3 | 348 |
| 4 | 2166 |
| 5 | 9528 |
| 6 | 44760 |
| 7 | 198816 |
| 8 | 877800 |
| 9 | 3809856 |
| 10 | 16379232 |
| 11 | 69769920 |
| 12 | 295055136 |
| 13 | 1239952512 |
| 14 | 5183031744 |
| 15 | 21564442752 |
| 16 | 89355535680 |
| 17 | 368925874944 |
| 18 | 1518322209600 |
| 19 | 6230763310464 |
| 20 | 25503209969088 |
| 21 | 104143201935360 |
[0,120,348,2166,9528,44760,198816,877800,3809856, 16379232,69769920,295055136,1239952512,5183031744, 21564442752,89355535680,368925874944, 1518322209600,6230763310464,25503209969088, 104143201935360] |