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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 28 |
| 4 | 336 |
| 5 | 5808 |
| 6 | 132000 |
| 7 | 3731040 |
| 8 | 126362880 |
| 9 | 4993309440 |
| 10 | 225677975040 |
| 11 | 11487263961600 |
| 12 | 650467886745600 |
| 13 | 40565803419187200 |
| 14 | 2763133948128153600 |
| 15 | 204127536266119065600 |
| 16 | 16257504491853520896000 |
| 17 | 1388699783389209747456000 |
| 18 | 126649067639795642253312000 |
[1,2,4,28,336,5808,132000,3731040,126362880, 4993309440,225677975040,11487263961600, 650467886745600,40565803419187200, 2763133948128153600,204127536266119065600, 16257504491853520896000,1388699783389209747456000, 126649067639795642253312000] |