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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 18 |
| 4 | 96 |
| 5 | 600 |
| 6 | 5760 |
| 7 | 57960 |
| 8 | 645120 |
| 9 | 8285760 |
| 10 | 117936000 |
| 11 | 1842825600 |
| 12 | 31374604800 |
| 13 | 578334556800 |
| 14 | 11493004723200 |
| 15 | 244720360684800 |
| 16 | 5555523785011200 |
| 17 | 134002274473267200 |
| 18 | 3422904611167641600 |
| 19 | 92290617116425728000 |
| 20 | 2619214995575033856000 |
[1,1,2,18,96,600,5760,57960,645120,8285760, 117936000,1842825600,31374604800,578334556800, 11493004723200,244720360684800,5555523785011200, 134002274473267200,3422904611167641600, 92290617116425728000,2619214995575033856000] |