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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 28 |
| 4 | 258 |
| 5 | 2318 |
| 6 | 19996 |
| 7 | 173042 |
| 8 | 1495602 |
| 9 | 12923884 |
| 10 | 111679970 |
| 11 | 965051522 |
| 12 | 8339221132 |
| 13 | 72061022634 |
| 14 | 622694890854 |
| 15 | 5380841364452 |
| 16 | 46497015154242 |
| 17 | 401790774458110 |
| 18 | 3471961070277860 |
| 19 | 30001967293824306 |
| 20 | 259253494870328354 |
[0,2,28,258,2318,19996,173042,1495602,12923884, 111679970,965051522,8339221132,72061022634, 622694890854,5380841364452,46497015154242, 401790774458110,3471961070277860, 30001967293824306,259253494870328354] |