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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 5 |
| 2 | 20 |
| 3 | 120 |
| 4 | 600 |
| 5 | 3120 |
| 6 | 15480 |
| 7 | 78120 |
| 8 | 390000 |
| 9 | 1953000 |
| 10 | 9762480 |
| 11 | 48828120 |
| 12 | 244124400 |
| 13 | 1220703120 |
| 14 | 6103437480 |
| 15 | 30517574880 |
| 16 | 152587500000 |
| 17 | 762939453120 |
| 18 | 3814695297000 |
| 19 | 19073486328120 |
| 20 | 95367421874400 |
| 21 | 476837158124880 |
| 22 | 2384185742187480 |
| 23 | 11920928955078120 |
[1,5,20,120,600,3120,15480,78120,390000,1953000, 9762480,48828120,244124400,1220703120,6103437480, 30517574880,152587500000,762939453120, 3814695297000,19073486328120,95367421874400, 476837158124880,2384185742187480, 11920928955078120] |