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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 6 |
| 2 | 12 |
| 3 | 42 |
| 4 | 120 |
| 5 | 366 |
| 6 | 1092 |
| 7 | 3282 |
| 8 | 9840 |
| 9 | 29526 |
| 10 | 88572 |
| 11 | 265722 |
| 12 | 797160 |
| 13 | 2391486 |
| 14 | 7174452 |
| 15 | 21523362 |
| 16 | 64570080 |
| 17 | 193710246 |
| 18 | 581130732 |
| 19 | 1743392202 |
| 20 | 5230176600 |
| 21 | 15690529806 |
| 22 | 47071589412 |
| 23 | 141214768242 |
| 24 | 423644304720 |
| 25 | 1270932914166 |
[0,6,12,42,120,366,1092,3282,9840,29526,88572, 265722,797160,2391486,7174452,21523362,64570080, 193710246,581130732,1743392202,5230176600, 15690529806,47071589412,141214768242,423644304720, 1270932914166] |