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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 90 |
| 5 | 352 |
| 6 | 1386 |
| 7 | 5504 |
| 8 | 21930 |
| 9 | 87552 |
| 10 | 349866 |
| 11 | 1398784 |
| 12 | 5593770 |
| 13 | 22372352 |
| 14 | 89483946 |
| 15 | 357924864 |
| 16 | 1431677610 |
| 17 | 5726666752 |
| 18 | 22906579626 |
| 19 | 91626143744 |
| 20 | 366504225450 |
| 21 | 1466016202752 |
| 22 | 5864063412906 |
| 23 | 23456250855424 |
| 24 | 93824997829290 |
[2,6,24,90,352,1386,5504,21930,87552,349866, 1398784,5593770,22372352,89483946,357924864, 1431677610,5726666752,22906579626,91626143744, 366504225450,1466016202752,5864063412906, 23456250855424,93824997829290] |