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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 306 |
| 3 | 5202 |
| 4 | 88281 |
| 5 | 1498176 |
| 6 | 25424928 |
| 7 | 431474688 |
| 8 | 7322358456 |
| 9 | 124264377216 |
| 10 | 2108833575552 |
| 11 | 35788044422016 |
| 12 | 607342437246528 |
| 13 | 10306929088604160 |
| 14 | 174914151758088192 |
| 15 | 2968387598501627904 |
| 16 | 50375140298107596288 |
| 17 | 854893330417826832384 |
| 18 | 14508001408391876911104 |
[1,18,306,5202,88281,1498176,25424928,431474688, 7322358456,124264377216,2108833575552, 35788044422016,607342437246528,10306929088604160, 174914151758088192,2968387598501627904, 50375140298107596288,854893330417826832384, 14508001408391876911104] |