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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 6 |
| 3 | 33 |
| 4 | 180 |
| 5 | 1024 |
| 6 | 5228 |
| 7 | 26670 |
| 8 | 134438 |
| 9 | 670407 |
| 10 | 3310176 |
| 11 | 16219930 |
| 12 | 78973826 |
| 13 | 382408399 |
| 14 | 1842856150 |
| 15 | 8843787665 |
| 16 | 42284752666 |
| 17 | 201514337962 |
| 18 | 957534960784 |
| 19 | 4537926120718 |
| 20 | 21454758254236 |
| 21 | 101215638872346 |
| 22 | 476553258095432 |
[2,6,33,180,1024,5228,26670,134438,670407,3310176, 16219930,78973826,382408399,1842856150,8843787665, 42284752666,201514337962,957534960784, 4537926120718,21454758254236,101215638872346, 476553258095432] |