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| n | a(n) |
|---|---|
| 1 | 21 |
| 2 | 441 |
| 3 | 1889 |
| 4 | 8465 |
| 5 | 50139 |
| 6 | 220882 |
| 7 | 891720 |
| 8 | 3919354 |
| 9 | 16153614 |
| 10 | 62844340 |
| 11 | 248939744 |
| 12 | 971561382 |
| 13 | 3682206767 |
| 14 | 13939172767 |
| 15 | 52509796817 |
| 16 | 195002378289 |
| 17 | 720554922955 |
| 18 | 2654209247431 |
| 19 | 9705662821905 |
| 20 | 35326530765908 |
| 21 | 128233462946586 |
[21,441,1889,8465,50139,220882,891720,3919354, 16153614,62844340,248939744,971561382,3682206767, 13939172767,52509796817,195002378289,720554922955, 2654209247431,9705662821905,35326530765908, 128233462946586] |