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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 21 |
| 3 | 181 |
| 4 | 1341 |
| 5 | 8312 |
| 6 | 44300 |
| 7 | 207562 |
| 8 | 872998 |
| 9 | 3348194 |
| 10 | 11857834 |
| 11 | 39165935 |
| 12 | 121628739 |
| 13 | 357500769 |
| 14 | 1000121700 |
| 15 | 2675524936 |
| 16 | 6872220036 |
| 17 | 17006979680 |
| 18 | 40673780258 |
| 19 | 94256429647 |
| 20 | 212145160692 |
| 21 | 464710684230 |
| 22 | 992576762139 |
[2,21,181,1341,8312,44300,207562,872998,3348194, 11857834,39165935,121628739,357500769,1000121700, 2675524936,6872220036,17006979680,40673780258, 94256429647,212145160692,464710684230, 992576762139] |