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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 22 |
| 5 | 166 |
| 6 | 1266 |
| 7 | 11166 |
| 8 | 106128 |
| 9 | 1122192 |
| 10 | 12809520 |
| 11 | 159451920 |
| 12 | 2128973760 |
| 13 | 30594214080 |
| 14 | 468275713920 |
| 15 | 7641089769600 |
| 16 | 131971588761600 |
| 17 | 2412294180710400 |
| 18 | 46422407927347200 |
| 19 | 940023724189132800 |
| 20 | 19949344876532736000 |
| 21 | 443393309963068416000 |
| 22 | 10288553164881868800000 |
[0,0,4,22,166,1266,11166,106128,1122192,12809520, 159451920,2128973760,30594214080,468275713920, 7641089769600,131971588761600,2412294180710400, 46422407927347200,940023724189132800, 19949344876532736000,443393309963068416000, 10288553164881868800000] |