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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 2 |
| 3 | 4 |
| 4 | 28 |
| 5 | 330 |
| 6 | 4750 |
| 7 | 80050 |
| 8 | 1559430 |
| 9 | 34631010 |
| 10 | 866193150 |
| 11 | 24128154570 |
| 12 | 741441847710 |
| 13 | 24926160803190 |
| 14 | 910288638654210 |
| 15 | 35889186812894250 |
| 16 | 1519450997661008550 |
| 17 | 68756119302418668000 |
| 18 | 3311679881316255436200 |
[2,2,4,28,330,4750,80050,1559430,34631010, 866193150,24128154570,741441847710,24926160803190, 910288638654210,35889186812894250, 1519450997661008550,68756119302418668000, 3311679881316255436200] |