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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 21 |
| 3 | 117 |
| 4 | 497 |
| 5 | 2577 |
| 6 | 13937 |
| 7 | 72541 |
| 8 | 375054 |
| 9 | 1951949 |
| 10 | 10170792 |
| 11 | 52930039 |
| 12 | 275412159 |
| 13 | 1433386475 |
| 14 | 7460147264 |
| 15 | 38825258091 |
| 16 | 202060807970 |
| 17 | 1051605128451 |
| 18 | 5472968149750 |
| 19 | 28483454530439 |
| 20 | 148239012444720 |
| 21 | 771493812884305 |
[1,21,117,497,2577,13937,72541,375054,1951949, 10170792,52930039,275412159,1433386475,7460147264, 38825258091,202060807970,1051605128451, 5472968149750,28483454530439,148239012444720, 771493812884305] |