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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 18 |
| 4 | 166 |
| 5 | 1740 |
| 6 | 20948 |
| 7 | 287784 |
| 8 | 4466712 |
| 9 | 77539680 |
| 10 | 1491571872 |
| 11 | 31532466240 |
| 12 | 727281881280 |
| 13 | 18184495230720 |
| 14 | 490130371249920 |
| 15 | 14170353892047360 |
| 16 | 437524311352665600 |
| 17 | 14370793956158976000 |
[0,0,2,18,166,1740,20948,287784,4466712,77539680, 1491571872,31532466240,727281881280, 18184495230720,490130371249920,14170353892047360, 437524311352665600,14370793956158976000] |