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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 5 |
| 2 | 18 |
| 3 | 78 |
| 4 | 408 |
| 5 | 2520 |
| 6 | 18000 |
| 7 | 146160 |
| 8 | 1330560 |
| 9 | 13426560 |
| 10 | 148780800 |
| 11 | 1796256000 |
| 12 | 23471078400 |
| 13 | 330032102400 |
| 14 | 4969162598400 |
| 15 | 79768136448000 |
| 16 | 1359981342720000 |
| 17 | 24542432538624000 |
| 18 | 467373280518144000 |
| 19 | 9366672731480064000 |
[1,5,18,78,408,2520,18000,146160,1330560,13426560, 148780800,1796256000,23471078400,330032102400, 4969162598400,79768136448000,1359981342720000, 24542432538624000,467373280518144000, 9366672731480064000] |