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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 9 |
| 3 | 51 |
| 4 | 335 |
| 5 | 2364 |
| 6 | 17511 |
| 7 | 134303 |
| 8 | 1057446 |
| 9 | 8498115 |
| 10 | 69424964 |
| 11 | 574844733 |
| 12 | 4813486921 |
| 13 | 40690941990 |
| 14 | 346798845213 |
| 15 | 2976661777689 |
| 16 | 25708160461067 |
| 17 | 223247734992435 |
| 18 | 1948116221860923 |
| 19 | 17073908081529946 |
| 20 | 150228705609723510 |
| 21 | 1326518390219586025 |
[1,2,9,51,335,2364,17511,134303,1057446,8498115, 69424964,574844733,4813486921,40690941990, 346798845213,2976661777689,25708160461067, 223247734992435,1948116221860923, 17073908081529946,150228705609723510, 1326518390219586025] |