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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 7 |
| 4 | 37 |
| 5 | 221 |
| 6 | 1801 |
| 7 | 15709 |
| 8 | 157641 |
| 9 | 1775521 |
| 10 | 21898801 |
| 11 | 296379931 |
| 12 | 4346295757 |
| 13 | 68682481141 |
| 14 | 1163591541113 |
| 15 | 21024039322441 |
| 16 | 403559222086801 |
| 17 | 8199021870113985 |
| 18 | 175746277620520417 |
| 19 | 3963144157484213359 |
| 20 | 93778090395227788021 |
| 21 | 2323080237693908254381 |
[1,1,1,7,37,221,1801,15709,157641,1775521, 21898801,296379931,4346295757,68682481141, 1163591541113,21024039322441,403559222086801, 8199021870113985,175746277620520417, 3963144157484213359,93778090395227788021, 2323080237693908254381] |