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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 12 |
| 3 | 54 |
| 4 | 240 |
| 5 | 1170 |
| 6 | 5330 |
| 7 | 24689 |
| 8 | 116890 |
| 9 | 549479 |
| 10 | 2578328 |
| 11 | 12131698 |
| 12 | 57065922 |
| 13 | 268256602 |
| 14 | 1261383897 |
| 15 | 5931754425 |
| 16 | 27891320698 |
| 17 | 131147135601 |
| 18 | 616682910805 |
| 19 | 2899744304684 |
| 20 | 13635001788168 |
| 21 | 64114012351029 |
| 22 | 301474577118884 |
[2,12,54,240,1170,5330,24689,116890,549479, 2578328,12131698,57065922,268256602,1261383897, 5931754425,27891320698,131147135601,616682910805, 2899744304684,13635001788168,64114012351029, 301474577118884] |