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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 25 |
| 5 | 114 |
| 6 | 560 |
| 7 | 2880 |
| 8 | 15321 |
| 9 | 83600 |
| 10 | 465322 |
| 11 | 2631668 |
| 12 | 15079922 |
| 13 | 87362184 |
| 14 | 510837760 |
| 15 | 3010987912 |
| 16 | 17870854206 |
| 17 | 106713713826 |
| 18 | 640659094566 |
| 19 | 3864643224900 |
| 20 | 23412690485800 |
| 21 | 142386465217920 |
| 22 | 868967571732540 |
| 23 | 5320093500153120 |
| 24 | 32666064906596550 |
| 25 | 201109232686971492 |
[1,2,6,25,114,560,2880,15321,83600,465322,2631668, 15079922,87362184,510837760,3010987912, 17870854206,106713713826,640659094566, 3864643224900,23412690485800,142386465217920, 868967571732540,5320093500153120, 32666064906596550,201109232686971492] |