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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 36 |
| 3 | 340 |
| 4 | 3220 |
| 5 | 30500 |
| 6 | 288900 |
| 7 | 2736500 |
| 8 | 25920500 |
| 9 | 245522500 |
| 10 | 2325622500 |
| 11 | 22028612500 |
| 12 | 208658012500 |
| 13 | 1976437062500 |
| 14 | 18721080562500 |
| 15 | 177328620312500 |
| 16 | 1679680800312500 |
| 17 | 15910164901562500 |
| 18 | 150703245014062500 |
| 19 | 1427481625632812500 |
| 20 | 13521300031257812500 |
| 21 | 128075592184414062500 |
[1,4,36,340,3220,30500,288900,2736500,25920500, 245522500,2325622500,22028612500,208658012500, 1976437062500,18721080562500,177328620312500, 1679680800312500,15910164901562500, 150703245014062500,1427481625632812500, 13521300031257812500,128075592184414062500] |