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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 18 |
| 3 | 141 |
| 4 | 984 |
| 5 | 6762 |
| 6 | 46365 |
| 7 | 317808 |
| 8 | 2178306 |
| 9 | 14930349 |
| 10 | 102334152 |
| 11 | 701408730 |
| 12 | 4807526973 |
| 13 | 32951280096 |
| 14 | 225851433714 |
| 15 | 1548008755917 |
| 16 | 10610209857720 |
| 17 | 72723460248138 |
| 18 | 498454011879261 |
| 19 | 3416454622906704 |
| 20 | 23416728348467682 |
[0,18,141,984,6762,46365,317808,2178306,14930349, 102334152,701408730,4807526973,32951280096, 225851433714,1548008755917,10610209857720, 72723460248138,498454011879261,3416454622906704, 23416728348467682] |