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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 76 |
| 3 | 376 |
| 4 | 1808 |
| 5 | 8736 |
| 6 | 42176 |
| 7 | 203648 |
| 8 | 983296 |
| 9 | 4747776 |
| 10 | 22924288 |
| 11 | 110688256 |
| 12 | 534450176 |
| 13 | 2580553728 |
| 14 | 12460015616 |
| 15 | 60162277376 |
| 16 | 290489171968 |
| 17 | 1402605797376 |
| 18 | 6772379877376 |
| 19 | 32699942699008 |
| 20 | 157889290305536 |
[1,18,76,376,1808,8736,42176,203648,983296, 4747776,22924288,110688256,534450176,2580553728, 12460015616,60162277376,290489171968, 1402605797376,6772379877376,32699942699008, 157889290305536] |