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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 53 |
| 5 | 1305 |
| 6 | 177559 |
| 7 | 247880897 |
| 8 | 9252468642944 |
| 9 | 39211218810149955871 |
| 10 | 155393322265527728403643204013 |
| 11 | 12102963126133848174768954972642433817636369 |
[1,1,2,7,53,1305,177559,247880897,9252468642944, 39211218810149955871, 155393322265527728403643204013, 12102963126133848174768954972642433817636369] |