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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 18 |
| 4 | 192 |
| 5 | 2500 |
| 6 | 38880 |
| 7 | 705894 |
| 8 | 14680064 |
| 9 | 344373768 |
| 10 | 9000000000 |
| 11 | 259374246010 |
| 12 | 8173092077568 |
| 13 | 279577021469772 |
| 14 | 10318292052303872 |
| 15 | 408700964355468750 |
| 16 | 17293822569102704640 |
| 17 | 778579070010669895696 |
| 18 | 37160496515557841043456 |
| 19 | 1874292305362402347591138 |
[0,2,18,192,2500,38880,705894,14680064,344373768, 9000000000,259374246010,8173092077568, 279577021469772,10318292052303872, 408700964355468750,17293822569102704640, 778579070010669895696,37160496515557841043456, 1874292305362402347591138] |