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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 7 |
| 4 | 49 |
| 5 | 301 |
| 6 | 2281 |
| 7 | 21211 |
| 8 | 220417 |
| 9 | 2528569 |
| 10 | 32014801 |
| 11 | 442974511 |
| 12 | 6638604721 |
| 13 | 107089487077 |
| 14 | 1849731389689 |
| 15 | 34051409587651 |
| 16 | 665366551059841 |
| 17 | 13751213558077681 |
| 18 | 299644435399909537 |
| 19 | 6864906328749052759 |
| 20 | 164941239260973870001 |
| 21 | 4146673091958686331421 |
[1,1,1,7,49,301,2281,21211,220417,2528569, 32014801,442974511,6638604721,107089487077, 1849731389689,34051409587651,665366551059841, 13751213558077681,299644435399909537, 6864906328749052759,164941239260973870001, 4146673091958686331421] |