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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 10 |
| 3 | 36 |
| 4 | 204 |
| 5 | 1104 |
| 6 | 7776 |
| 7 | 57600 |
| 8 | 505440 |
| 9 | 4803840 |
| 10 | 51442560 |
| 11 | 597784320 |
| 12 | 7609593600 |
| 13 | 104364288000 |
| 14 | 1541746483200 |
| 15 | 24329797632000 |
| 16 | 409042632499200 |
| 17 | 7290954768384000 |
| 18 | 137384159367168000 |
| 19 | 2727604332085248000 |
| 20 | 56913717580296192000 |
| 21 | 1244955414746824704000 |
[1,2,10,36,204,1104,7776,57600,505440,4803840, 51442560,597784320,7609593600,104364288000, 1541746483200,24329797632000,409042632499200, 7290954768384000,137384159367168000, 2727604332085248000,56913717580296192000, 1244955414746824704000] |