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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 25 |
| 5 | 124 |
| 6 | 738 |
| 7 | 5136 |
| 8 | 40922 |
| 9 | 367218 |
| 10 | 3664224 |
| 11 | 40240560 |
| 12 | 482278326 |
| 13 | 6263414736 |
| 14 | 87618506160 |
| 15 | 1313435465280 |
| 16 | 21003904630824 |
| 17 | 356910121855320 |
| 18 | 6422020465846320 |
| 19 | 121980351190294800 |
| 20 | 2438956634267865720 |
| 21 | 51206322309647263200 |
| 22 | 1126314497201852150640 |
[1,1,2,6,25,124,738,5136,40922,367218,3664224, 40240560,482278326,6263414736,87618506160, 1313435465280,21003904630824,356910121855320, 6422020465846320,121980351190294800, 2438956634267865720,51206322309647263200, 1126314497201852150640] |