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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 18 |
| 3 | 260 |
| 4 | 4890 |
| 5 | 110124 |
| 6 | 2844772 |
| 7 | 82196424 |
| 8 | 2613699450 |
| 9 | 90450874860 |
| 10 | 3379153837180 |
| 11 | 135445714293720 |
| 12 | 5796441493971284 |
| 13 | 263784018974675416 |
| 14 | 12721572505160772840 |
| 15 | 648250134428292640272 |
| 16 | 34809708051186914034730 |
| 17 | 1965040180185473309749788 |
| 18 | 116359823755204505172646204 |
[1,2,18,260,4890,110124,2844772,82196424, 2613699450,90450874860,3379153837180, 135445714293720,5796441493971284, 263784018974675416,12721572505160772840, 648250134428292640272,34809708051186914034730, 1965040180185473309749788, 116359823755204505172646204] |